Dont they hold them and release them when they are being reset and share that knowledge with a select few?
Also it wouldnt be irrational by any means that they wouldnt disclose that information with there friends and see that info on whats being reset and decide "Hey hmm I like this tag, I think I might take it." While no one else has the opportunity because its first come first serve.
I had a personal contact that told me those tags are from the original xbox live beta in 2002-2003 (I believe thats the time when it was beta testing) and the users never switched them to a email so those accounts arent even linked to a email address. Dormant accounts arent always dormant they are being held pick and choose for unique or priviledged members.
"Those accounts arent even linked to a email" - Xbox Represenative
The rest was my own speculation, it would be strange if this was true although I need to confirm this with an actual beta tester in those days.