I think something similar may have happened to me, due to something I probably did a long time ago. I think way back then I may have registered my tag in the brand new IL2 (forums or whatever) that took place after the original IL2; that might have happened even before RoF came about.
All I know is that when I tried to register much later, it would tell me that my email (or even password) was already in use. I was like, really? Somebody is using my exact same email and/or password? Then I realized that it had to be me, but that their stupid system could not differentiate between that and what happened 5 years ago; in essence, "JG1_Luftritter" was already taken. So I couldn't create an account using the name that I wanted to.
In any case, I had to play around with exactly how the squadron was named, together with my pilot name; and there are rules, like you can't have a "leading underscore" in your pilot name....which basically made it impossible to to use the simple "JG1" as my squadron.
In the end, I think I used that then-acceptable "II./" as my squadron, and the "JG1_Luftritter" as my pilot name; where as in RoF, my name was all one "JG1_LuftritterJ4", denoting my squadron, as per the current squadron rules on the WWI side.
However now, the limitations of the all-encompassing game do not really accommodate both WWII and WWI separation of names; and so the standard that we are using because of that is simply the squadron with pilot name, in order to take into account everything.
So, even though that this would not allow me to use a name that is simply "Luftritter", "LuftritterJ4", or "_Luftritter", it would allow me to register with a BLANK squadron field, and a pilot name of "JG1_Luftritter", which I could not do in RoF, because there were too many characters.
So apparently you have to play their stupid game, rather than hoping that they'll someday recognize your own old credentials as your own.