Hello Jason
That is an interesting discovery. It seems that there is an internal counter that the device uses to keep track of how many configs have been backed up. That counter seems to be reset to 0 once the device has been reloaded, so you can eventually get more than 14 backup files.
One thing you can do to test this theory is to issue the show archive command. This provides information about the existing configuration archive files. This command will list all the archived configurations along with their index numbers. By counting these, you can determine how many archives are currently stored. You can compare this with a list of the actual files in the flash. After a reboot, see if the list in the output and the actual files in the flash correspond to each other. If there are more files in the flash, then those backups that were made before the reload are indeed not kept track of as far as the maximum archive count goes.
Take a look at this command reference for more info on the show archive command.
https://www.cisco.com/c/en/us/td/docs/ios/fundamentals/command/reference/cf_book/cf_s1.html#wp1072078
Unfortunately, there’s no command that explicitly tells us the current counter of archives. Try this out and let us know your results.
I hope this has been helpful!
Laz