My gg grandfather registered the births of multiple children (including some who were already deceased) at one time a few years after some of their births. There is a note in the records that the reason for the delay was his constant traveling.
We know he was involved in textile trade in the area around Lodz and assume that he often traveled for work reasons. This also could be why there are contradictory records for his childrens' births listing both Belchatow and Zloczew as the birthplaces, while family lore was always that the family was from Lodz.
Something to consider is that people were more mobile than we might assume. Travel took longer but was still done. Something as simple as traveling could be a reason for delayed registration.