Consider the scenario where I delete my wallet then restore it from the seed phrase. Now all sub-addresses are lost. Then, I recover my sub-addresses by other means (e.g. logs). Can I verify that they actually belong to my wallet, and can I add them back to my wallet to use them again?
When restoring a wallet from seed phrase, you do not lose your subaddresses. This is because subaddresses are deterministically derived from you wallet keys. Therefore there is never a scenario whereby you would need to restore subaddresses "by other means" or " add them back to my wallet". By restoring a wallet, you have all the subaddresses too.
Getting technical, it is also possible to verify if you own a given subaddress. To do this you would need to create all the subaddresses that cover the range of possible indexes of the subaddress you wanted to check for a match. E.g. if you knew your wallet only had 2 accounts and up to 100 subaddresses, you would create the first 100 subaddresses for account 0 and account 1, then one of those will match the address you are checking.