Are you absolutely sure that all those wallets aren't just password-protected with no receiving addresses created for it yet? 

Core doesn't create receiving addresses for new wallets by default, you have to explicitly tell it to give you an address so it's possible the wallets you're trying to dump were only created but never used (by virtue of having not receiving addresses for it).

As far as looking for the private key is concerned, look for something with "5H" "5J" "5K" or "5L" at the beginning of a line.

[ I believe the 70 found "wallets" were probably the empty .dat files created by PYwallet when I ran it (probably 70 times)!!

 I thought that bitcoin core automatically creates one wallet when installed, I wasn't trying to dump wallets as I don't know how, was just trying to find a wallet then go to the next step of extracting keys and........ so now I'll plug in a drive with electrum wallet and a backed up bitcoine core wallet to test the PYwallet again to see if PYwallet works as designed on my machine, I also just learned that it doesn't look into compressed files, back up files in their current status no wonder I can't find any wallets will have a long way to find good quality programs to decompress and decipher/make backup files readable to PYwallet, I was using windows search looking for .dat files on a 500 GB drive yesterday and it said it needs 1.4TB disk space
.]