My understanding is that a siyum should be made on the last bit of the text being studied. Thus, if the entire Mishna (all six "orders") is studied for someone's yahrzeit, the last mishna (individual piece of the Mishna) to be studied should be the one studied as the siyum.
It often occurs that many people band together to complete the Mishna before someone's first yahrzeit. There's a sign-up sheet, which says something along the lines of "Please complete your portion by [the yahrzeit]". And on the yahrzeit, someone completes the last bit at a meal.
But that meal is not always in the last minute of the day. So those finishing "by [the yahrzeit]" may not have finished their respective portion. How, then, does the one who's completing the last bit know that everyone's done by that time?
- Does he not, and take his chances?
- Does he hold the siyum after the yahrzeit?
- Do those studying understand, generally, that they should finish before (and not on) the yahrzeit? (I haven't understood that!)
- Does he call all those studying to see whether they've finished their respective portions and, if not, ask them to do so before x o'clock on the yahrzeit when the siyum will be made?
- Or what?
Any sources, experience, anecdotes, etc. will be appreciated.