I used the menu.

The only wallets I have are the current encrypted ones. There are no other wallet.dat files anywhere, no backups or previous versions laying around.
I figured for security reasons I wouldn't keep an unencrypted wallet sitting on my harddrive.

Now that you mention it, I don't believe I have.

Although it is possible I messed up inputting the passwords, I was incredibly careful, and for it to happen to two different wallets is just incredibly bizarre.
I don't believe it is a minor typo however, as I've already extensively ran btcrecover on both wallets with a variety of different approaches to check for typos.

Unfortunately there are no earlier versions of the wallets.
Once I encrypted the wallets, I emailed them to myself and those were the only backups I had.

Not the same password for both, but the same structure for both. The chances of mistyping both are extremely low considering how careful I was.

What is the possibility the .dat file is merely corrupt and no password will be accepted?

So I open up my wallets today and uh oh, my passcodes don't work at all.
A few months ago, I added passcode-encryption to two different wallets on Bitcoin Core v0.15.1 and Litecoin Core v0.14.2.
Both have the same issue today: it simply says the passcode is incorrect and won't let me send transactions or change the passcode.
Also to clarify while its the same passcode structure for both, they are two different passwords.

I created a very deliberate passcode system and was very careful when doing so. All instructions were written down on paper so I wouldn't forget it.
I also made a new wallet with a similar passcode system and it worked as normal, so I am very perplexed right now
I even ran a python brute force to guess my passcodes with token typos just in case, but no luck so far.
My only conclusion is that somewhere between encrypting and backing up these wallet files, something went wrong, but I'm not sure what exactly.
One last thing worth mentioning is that both passwords include the characters "%" and "#", in case that could be causing an issue.

Any advice or ideas would be greatly appreciated, because aside from more brute-forcing I really have no idea what to do here.

Thanks.