Keep one backup in your house, and another at a trusted relative’s house or a safety deposit box. Fire and theft are real risks.
After you send a large transaction (or create more than 100 new addresses), you must create a new backup. Due to how the keypool works, a very old backup might not contain the private keys for your most recent addresses. Bitcoin Core Wallet.dat
You can rescan and prune using the -rescan and -reindex commands, but the cleanest solution is to create a new Wallet.dat file ( File -> New Wallet ), send all your Bitcoin to the new wallet, and delete the old one. This leaves the old history behind, resulting in a tiny, fresh file. Keep one backup in your house, and another