The private keys you mention are in WIF(u) format. In HEX format 64bits they are in fact the very first few addresses like 000000000000000000000000000000000000000000000000000000000000001a

It is known that these adresses had been used early on in bitcoin history, some even date from 2017.

Now, you also say that you found other private keys corresponding to addresses used this year. This part is interesting: could you olease post a few examples? It could be possible that some early users haven't updated their software and still ise a faulty one.