Lot traceability for small manufacturers: backward, forward, and a recall drill

A supplier calls: the steel you received on the 4th was out of spec. The only question that matters is which units it went into and who has them, and you have about a day to answer it. This page is about being able to — what a lot is, where it has to be captured, what "trace backward" and "trace forward" mean for a product built from parts, and the difference between an answer you can stand behind and one you inferred.

Reading this for your own shop? Start a free 14-day trial — no credit card, and your data is yours to export at any time.

1.The short answer

A lot is a quantity of one material that shares an origin — a supplier's batch, a delivery, a coil — identified by a lot number captured when it is received, with an expiry date if it has one. Traceability is being able to follow that lot both ways:

• Backward: from the lot to the receipt that brought it in — supplier, date, purchase order, quantity, expiry.
• Forward: from the lot to everything that consumed it — the work orders, the finished units built from it, and the customers who received those units.

For a distributor the forward trace is one step: lot to sale. For a manufacturer it runs through the bill of materials, and that is the part that needs the work order to record which lots went into which units — genealogy. Everything else on this page is the difference between having that record and not.

2.Where the lot has to be captured

Traceability is only as good as the moment of receipt. If the lot number on the supplier's label is not recorded when the steel comes off the truck, nothing downstream can recover it. So the first setting is per item: lot-tracked, which makes a lot number required on every receipt of that item. A receipt with no lot is refused, not accepted with a blank — a blank lot is the one you find during the recall.

Not every item needs it. Fasteners bought by the thousand from a catalogue probably do not; the structural material, the coating, the component with a safety function, do. Mark the ones whose failure would have to be explained, and leave the rest, so the receiving screen asks for a lot exactly when it matters.

From then on each lot has a ledger of its own: received on this date with this expiry, this much still on hand, this much consumed and by what. The expiry date drives an expiring-soon report and the order the shop should use stock in; more on that below, because it also decides how much of a trace is exact.

3.Backward: from lot to supplier

The easy direction. Search the lot number and the trace returns the receipt rows that created it: purchase order, supplier, date received, quantity, expiry. If the same lot number arrived on two deliveries, both show. This is what you send back to the supplier who called, and what an auditor asks for first.

4.Forward: from lot to customer, through the work order

The hard direction, and the one with a distinction worth understanding. A lot leaves stock in more than one way, and they are not equally traceable.

Exact: the lot was scanned into the job

A routing step can require a scan. When it does, the operator records one unit at a time — "record unit 7" — and scans the component going into it, so the scanned lot is bound to unit 7 of that work order. When the order completes, unit 7 gets its serial number, and the binding carries across: lot → work order → unit 7 → serial. Search the lot and you get the serials that contain it; search a serial and you get the lots inside it. This is the answer you can stand behind, and it is exact because a person scanned a label at the moment it mattered.

Exact: the lot was picked at shipping

A sale is recorded too. Shipping a lot-tracked item asks which lots are going out, with the earliest expiry proposed; the lots picked are stored against the sale, and the trace marks that row exact. Where nothing names a lot — a spreadsheet sales upload, say — the earliest-expiry lot is assigned and recorded, and the trace marks it as assigned automatically, so you can tell a pick from an assumption.

Inferred: the lot was consumed without being recorded

Some stock still leaves without a lot attached — a component backflushed at completion, an adjustment, a sale recorded before lots were. The trace still attributes those consumptions to lots, but by first-expiry, first-out: it assumes the shop used the lot expiring soonest first, and works forward through the lots on that basis. That is an inference. It is right for a shop that actually ships oldest-expiry first and wrong in exactly the cases where someone reached for the nearer pallet.

5.The recall drill

Run this once before you need it. It takes ten minutes and tells you exactly where your traceability stops.

1. Pick a lot that arrived a month ago — steel lot S-2409-17, say, received on the 4th against a purchase order, 200 sheets.
2. Trace backward. Supplier, PO, date, quantity, expiry. Write down what you would send the supplier. If the lot number is missing or was typed from memory, stop: fix receiving first.
3. Trace forward. The lot's ledger shows 174 sheets consumed by work order WO-0388 (shelf units, 80 planned) and 26 still on hand. Open the work order's genealogy: the cutting step required a scan, so sheets from S-2409-17 are bound to units 1 through 80, and each unit has a serial.
4. Find the customers. Each finished unit has a disposition: shipped (to a named customer, on a named order), allocated to an order not yet shipped, or in stock. The eighty serials resolve to: 50 shipped to one customer on the 19th, 20 shipped to another on the 23rd, 10 in stock. That is the recall list, and it is three lines.
5. Note what was inferred. The 26 sheets on hand were also used for a repair job that had no scan step. The trace attributes that consumption by FEFO. Decide whether that is acceptable for the repair line; if not, add the scan step. That decision is the output of the drill.

Compare that with the drill without traceability: "we received some steel around then; it went into whatever we built after the 4th; we shipped about 300 units since." The recall is every unit, the customer call is every customer, and the cost is not the steel.

6.Serials: the customer's half of the question

A lot trace tells you which units contain the lot. A customer holding a unit asks the opposite: is this one affected? That needs the unit to have a serial the customer can read, generated when the unit was completed, unique, and linked to the genealogy. A serial recipe per product — prefix, date code, counter — gives every completed unit one without anyone typing, and the same search box that takes a lot number takes a serial.

7.What to set up before you need it

• Mark the items that matter as lot-tracked, so receiving refuses a blank lot for them. Start with anything structural, anything with a shelf life, and anything a customer could be hurt by.
• Capture from the label, at the dock. The lot number is whatever the supplier printed; a scanner or a phone camera gets it right, memory does not.
• Put a scan step on the routing for the components you would need to trace exactly, so the work order binds them to units. One step on the right operation converts inference into evidence for the whole product.
• Give finished goods a serial recipe, so completion issues one per unit and the customer can name theirs.
• Use stock oldest-expiry first, and say so on the floor. It is good practice on its own, and it is what makes the inferred part of a trace true.
• Run the drill once a quarter on a random lot, and fix whatever it shows.

8.Questions people ask

Does a lot have to have an expiry date?

No. The lot number is what traceability needs; the expiry is optional and drives the expiring-soon report and the FEFO order. Items with a shelf life can default an expiry from the receipt date so it is not typed each time.

What about sub-assemblies we make ourselves?

A sub-assembly built on a work order carries its own genealogy — the lots scanned into it — and its serial can be scanned into the parent's work order like any other component. A lot in the bracket steel then resolves to the bracket serials that contain it, and a bracket serial resolves to the shelf unit it was scanned into. The trace is as deep as the scan steps go.

We are not regulated. Is this overkill?

It is one setting per item, one scan per unit on one step, and a serial recipe. The day it is needed, it is the difference between recalling eleven units and recalling everything you built that quarter. Regulation, where it applies, only sets how quickly you have to be able to say which.

Can the trace be exact for sales, not just work orders?

Yes. Shipping a lot-tracked item records the lots it drew from — picked by the person shipping, or assigned earliest-expiry-first and labelled as such when nothing names one — so the forward trace lists each order it went out on as exact. Sales recorded before lots were recorded at shipping are shown as estimated, attributed first-expiry-first-out, and should be read that way. For a manufactured product the exact record is also the finished unit's serial, which carries the lots scanned in at the work order.