It's not like bitcoin core has a button you click and it prints out 10 neatly formatted private keys for you. Specially in early versions. You would have had to export them, format them in a way you could split it (as OP claims has done) and then print it out.
i'm sure it cant be that hard. all you need is a printer and copy/paste. even if it's 100 keys, that's maybe 3 sheets of paper max.
Besides why do you think OP means 10-20 keys when he uses the term "quite a bit"? It may be a lot more...
i don't think he ever even used his bitcoin. he just mined it and let it sit. so i doubt he has very many keys.
Mined quite a bit of Bitcoin way back at the beginning. Socked it away on a HDD, as well as on a flash drive in normal fashion, and paper backups.