Wallet file can corrupt, that is why it is good to backup your private key. This time that we have seed phrase, it is better to use seed phrase wallet (HD wallet), you will be able to just backup words instead. I thought bitcoin core is the wallet using wallet.dat for file backup, but I do not know about doge, but if it is bitcoin or doge, the backup would have worked if not corrupt.
Dogecoin code was built on C++ which is same to Bitcoin that's why they have similarity on wallet format during there early stage. And also this thread was a help thread for recovering old wallet, So suggesting the use of recovery seed instead is not appropriate since we all know that recovery seed is a bit standard nowadays for all types of wallet.