Next number in address book - large gaps in sequence?

I noticed we’re up to 391669 for address book next number.
It was at 310032 on January 7 which is a difference of 81,637.
It’s impossible we’ve added 81,000 addresses.
It seems that whenever a user/job adds an address for Customer, Vendor, Charitable Org, Vendor A/R, etc it creates a large gap in sequence number when the next user/job adds a different search type/UDC address record.

Not sure why it’s doing this and it doesn’t seem to be an issue – just odd.

We have users adding various address types and we have the batch address book batch upload that runs nightly.