I have a bit of experience of that, jno, from outside AB.
Within AB I did correctly 'out' around 60 users (well one actually with over 60 different names) who were then banned/suspended- they were easy to spot largely because without realising it they kept using the same phrases, formatting etc.
Most new users are genuine but when a new user comes on and starts making lots of posts, seems to know a lot of the history and immediately launches into other users I think many of us can spot they are an old user under anew name, but generally I don't know who they were.
She was so nasty to someone who put a question in Insurance. Obviously she doesn't consider that any poster on the net could have learning difficulties and what May seem like an absurdly stupid question to some, could seem perfectly bone fide to others.