idk if i should ask that here or somehwere else but..

[mostafaaph]

is there anyway to know someone's older battletags if you know the current battletag

 

[Wunderkind]

Banned - Banned until resolved - https://www.epicnpc.com/threads/wunderkind-scam-of-755.2849834/

is there anyway to know someone's older battletags if you know the current battletag

Not doable. Only Blizzard is able to check the battletag history.