okay i have contacted xbox an unbelievable amount of times, they say different stuff a lot of the times, but here is what happens with a gamertag from my experience, i might be wrong:
After 9 years of an inactive account, is is locked. Nobody can use it and nobody can get a hold of it. it takes this process SIX more years. after, you can take the account
i asked xbox what this process is even for and they responded with "security."
you know a tag is reset when it is OG and you can get it as your name lol
resets happen after an inactive account, and after the 6 year security process.
idk if this was what you were asking or not, if not, sorry. :\