Regarding berkley db, I found some article about that and I recovered several .dat files with that signature. I tried to open with pywallet --dumpwallet and they gave an error like invalid or corrupt database but one had 16kb and returned sth like PAGE_NOT_FOUND. Should all wallets be openable with pywallet or are the wallets specific to the tool which generated it? Maybe the PAGE_NOT_FOUND indicates that it is a berkley db but I'm using the wrong tool to open it?
All wallet.dat's are Berkeley DB's... but not all Berkeley DB's are wallet.dat's...
That is to say, just because you found a "random" .dat file that is a BerkeleyDB formatted file, does not mean it is a wallet.dat... what sort of filenames did these recovered files have? or did the recover software just find "random" file names?
Has your friend been actively using that HDD since the file was deleted
over 10 years ago??!? (from 2009/2010)
If so, the chances of recovering anything useful from "deleted files" is pretty much zero
Or has the old HDD just been sitting around gathering dust?