Largest complete panel obtainable under a coverage requirement.
A blocked design needs a complete matrix, but entries that joined a campaign late are scored on fewer periods than the rest. Admitting them costs periods for everyone, and excluding them costs entries. This helper makes that trade explicit and repeatable: keep the entries scored on at least min_periods periods, then keep the periods scored for all of them.
Raising min_periods admits fewer entries over a longer window, lowering it admits more entries over a shorter one. Neither direction dominates, so a campaign report is usually clearer with two or three panels bracketing the trade than with one.
This is pure: no logging, no plotting, no mutation.
Minimum number of scored periods an entry needs to enter the panel. Defaults to None, which admits every entry and therefore keeps only the periods scored for all of them.