How should I reconcile one completion with two saved rows?

The PLC retains a job counter. The monitor stores it in each row, but its duplicate check lives only in memory. Both saved rows have the same counter.

Then you've got something firmer than the time column to compare; does that counter ever start again?

We got caught by that with a test logger. A counter was unique until the equipment restarted. What did your PLC do during this particular outage: remain running, or restart as well?

Good distinction, I was assuming only the laptop had gone away.

Only the laptop disconnected in this test. The PLC kept running. Its counter can be reset during maintenance, though, so it is not a permanent unique identifier by itself.

I'd mark this pair as one known duplicated result and leave the wider restart case explicitly unfinished.

Please include the operator view. Two rows corrected in the database can still leave an instructor with a misleading total on screen. One explanation for both (and somebody responsible for making the correction).

What prevents a later legitimate job with a reused counter from being silently discarded by the proposed fix?

Nothing in my first suggestion covered that, you're right; the counter needs a run identity or an equivalent documented boundary.

I have added a proposed controller-run identity to the interface review. For the existing data, only the observed reconnect pair is being reconciled. Unknown matches will be flagged for review instead of discarded.

Also try losing the connection after the row is saved but before the monitor records that it handled it. That's where our logger duplicated things even with a good job identifier.

That reproduces the problem too. We are changing persistence so recognising an already recorded result does not depend on the monitor reaching a later in-memory step. No new work is submitted during recovery.

The laptop reconnect cases now display one completion in our offline tests. Maintenance reset handling still needs the PLC owner's review, so I am keeping the issue open on the handover sheet.

Does the instructor see the unresolved state after a counter reset, or is that still only in your log?