The ID is a big deal if you go online in sysnand. Thats exactly what got me banned in Smash bros just by clicking the online option in the menu. B/c the copy I paid for did not match the unique ID of the save file that I got from someone else. This only matters if you ever decide to do online battles. The ID is generated by the game itself
Are you saying that your issue was because you used the save from someone else and there were more than 1 save files with the same save ID connecting to the servers?
Because if not I find it hard to believe that it would be down to the fact that the game didn't match where the save came from. What if you have the game and then sell it and buy it again down the line? That shouldn't be the reason for a ban.
I know that modified Smash saves had a high risk of being banned from online because there was a bunch of information from those saves that was sent so they could see if they had been tampered with in certain ways.
Mainly questioning it because I moved my leaked Let's Go Eevee save data to my legit cart and never had any repercussions after going online, and I've done the same with Sword and haven't had any issues with that thus far either.