The thing is though i'm not sure which wallet exactly has all these coins either because this qt-wallet.dat was the one i used for my payment processing on mmoclub.com years ago and it just generated new wallet addresses for receiving everytime someone placed an order to identify them uniquely.
For that, you just have to load the wallet to Bitcoin Core and the correct balance should be displayed after it sync to the network
or if you already have a fully synced non-pruned Bitcoin Core, it only needs to be rescanned.
Even though it looked like it just generated an address whenever it needs a new one, it already has thousands pre-generated in the background which will be included to the scan.
Just for clarification, you said "
qt-wallet.dat" in your post but in the title it's "
wallet.dat", what's your wallet file exactly?
The former can be Bitcoin Core's wallet.