I am on 9.2, luckily! Idk, I was confused because in this topic (
http://gbatemp.net/threads/guide-the-emunand-save-data-mega-guide-gbatemp-doesnt-deserve.378491/) where it says " Basically, if
you want to continue to be able to play
retail games with >6.0 save encryption, you need to
stay on the system NAND version you are currently on. You'll need to stay at that system NAND
version until gateway fixes all of these save compatability issues."
So being on EmuNAND solves this? So I can only play my retail cart and .cia games on EmuNAND? The sysNAND 4.x will be basically useless besides being used to install all this stuff?
I didn't remember the issue with save encryption, as it has not personally affected me yet. My bad.
I'm not 100% sure about this, as I have currently never been above 4.5 sysNAND or emuNAND, but basically I guess the problem is a key used for signing saves with 6.0+ encryption is loaded when the console boots and is not reloaded by emuNAND booting.
So, in other words, your sysNAND needs to be the same as it was when you made the retail cart save (or at least within a compatible range). At least I think that's the basics of it.
In your case, you made your retail saves on a newer firmware sysNAND, so I don't think they will work if you downgrade your sysNAND to 4.x
BUT in theory you could downgrade to 4.x temporarily, install the legit .cias, then update your sysnand back to 9.2 in which case I think your retail saves would work again (not 100% on that, but it seems like it should work). The tricky part would be updating back to 9.2, since nintendo's servers would only officially give you the 9.6 update files.
I think you would have two options for getting back to 9.2 - 1.) there are apparently certain copies of SSB4 that have 9.2 on them. You could maybe get a retail cart of this if you are in the right region (not sure which region, but you should be able to find out with a search about "smash bros 9.2 update") 2.) I think you could use this program -
https://gbatemp.net/threads/3dnus.376488/ to download the necessary .cia files to update from 4.x back to 9.2 (I'm not actually sure if this works, but if you can install update from other regions with that program I don't see why you can't use it to manually update to any version)
I have not actually done any of this and I'm just writing based off what I've read here on gbatemp, so do not take my post as 100% fact. I recommend reading a bit more around gbatemp before you try anything, and good luck.