I made some paper wallets recently using bitcoinpaperwallet.com's offline generator. I tested decryption right after i made them and they opened just fine. After a few days, I try to open the same one again with the same passwrod, and it says invalid passphrase. This has happened before but I thought it was me forgetting the password. I don't think this is the case now. I'm wondering if anyone else has noticed this and what the solution is. This happens with both bitaddress.org and bitcoinpaperwallets.com (and makes sense as they both use the same code).
I too have some from years ago and i am fairly sure I had the correct password but no go.
Let me know if you figure it out.