Employer replaced my Apple Air with a MacBook Pro. I had been backing up to a 2 TB Time Capsule. When connecting to it the first time I selected "inherit" and thought things were working. Checked my backup tonight and it says it can't back up, not enough room. I thought Time Capsule tosses the oldest to make room for the new. Digging deeper it says my oldest backup is March 4 (says that's also my last backup). I open Time Capsule and lo and behold, years of backups are gone, March 4 is it. But it shows last update March 12 (but tonight I get alerts every few minutes saying the automatic backups aren't happening. My wife has had this problem for a couple of months. What are we doing wrong?
Time Machine backups are per-machine. You can't merge the data from your old MacBook Air with the backup for the new MacBook Pro. (Whilst there are technically methods for doing this they are almost universally a bad idea and carry a significant risk of corrupting the old backup and creating a ton of bloat for any future restore. See: Is there a way to merge Time Machine backups?.
If you still have the .sparsebundle file for the old MacBook Air and the encryption password (if set). You should archive this (somewhere that isn't the time capsule) so that you can access this data if required. You should then have enough space to instruct your new MacBook Pro to backup to the Time Capsule.
To check the actual backup files you should open the Time Capsule directly in Finder. Based on what you've said thus far I'd expect to see the following:
- MacBook Air Sparsebundle
- MacBook Pro Sparsebundle
- Wife's Mac Sparsebundle
You'll want to copy the MacBook Air Sparsebundle somewhere safe - this is essentially your long-term backup containing all the backup history from your old MacBook Air.