it has to be inactive for 7 years before it will get reset, one way to tell on certain tags how long theyve been inactive is to go to bungie.net, go to halo 2 type the tag and if it shows up, go to matchmaking history, and see what the last day it played was...
like i have the gt s e i z e
http://www.bungie.net/stats/PlayerStatsHalo2.aspx?player=seize&sg=3
its been inactive since 4.28.05 so mine will get reset sometime this year

it doesnt work on every tag because not everyone played halo 2 but if your lucky they did.....
a v1 tag is an original xbox gamertag