Do they use the same PERS department for handling the paperwork or no?
They all fall under NRC and same group of people type up the results, but there are multiple people that work at NRC and only one is needed to type up the results for each board to send it for signature. You could have half a dozen designators drop their board results on NRC on the same day and they would have no issues having people to work on them.
The other thing is realistically the SNA/SNFO board was done before AVO, the SNA/SNFO board takes only a day to make the picks, the rest of the time is figuring out OCS dates, verifying they didn't put another designator above SNA or SNFO, misc admin items. That is what takes up nearly all of the wait time. A smaller designator selection can get done later but have results released quicker due to smaller numbers.