Is it possible to track what tabards you have owned for Twenty-Five Tabards. If not the only other way i can think is to see what ones you currently own, and then buy the ones you you dont have, again.
Ah I see, sorry. I would suggest buying them again to make sure though. The only ones that could be difficult would be the ones requiring honor, BG marks... whatever else they have out there. Also, the vendor in the Visitor Centers sells tabards you're entitled to have. You could check there. For me, the one in IF had more tabards for sale than the one in Dalaran though... for some reason.