Side account, aside from being openly linked to your main is also legit (or appears to be).
Shells are empty, never linked, and almost always illegit (since they're stolen, ). Even if they aren't stolen and you made them, they're still illegit because you're not declaring them as sides to your main. Shells you always try to keep down low and away from TNT and the public.
What others have said though, if you're confident the original owner of a shell will never come back for their account and you change account info on a shell to a side (without being iced), then it can be made a side.
The Following User Says Thank You to Mod For This Useful Post: