Could be the females can retain the sperm for some time. So a single female that had been with a male may still be able to lay eggs for some time. Just a guess. But mollies do this and mystery snails do too.
20g L174/L46/RCS/hastatus/pygmy corys, 10g OEBTs, 10g blue bees, 10g CRS, 15g L316/L46/Amano shrimp, 10g black darter tetras/CPDs,15g ADFs/clown plecos, 25g L134s/CPDs/otos, 29g Weitzmani/panda corys/zebra otos, 46g CAE/L134s/CPDs/salt and pepper corys/BNs, rubberlip pleco, 55g SAEs/L201s/L199s/BNs/kissing gourami, 75g L316s/BNs/mix of old fish folk, 30g L340s/L211/tangerine tiger shrimp, 10g micro rasboras/CPDs, 20g L134/habrosus corys/RCS