just wondering if core creates another 100 address after 1st 100 are used or does it just generate them as required after that?
Actually it generates addresses as they are being used to maintain 100 unused addresses in reserve. So after you use one address, another one is generated so that there are still 100 remaining in reserve. After you have used one hundred addresses though, the backup that you previously made then is no longer valid since any further addresses were generated after your backup.
