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/hastatus/pygmy corys/L340 fry, 10g OEBTs, 10g blue bees, 10g CRS/sea sky blue shrimp, 15g L46/L340/L316 fry, 10g yellow/leopard shrimp, 15g ADF/clown plecos, 25g L134s/CPDs/otos, 29g Weitzmani/panda corys, 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/black darter tetras/CPDs/micro rasboras/L316 fry,10g tangerine tiger/snowball shrimp, 20g L134/habrosus corys, 10g CPD fry