The reset bag resets ev's only, when ev's reset it can gain ev's again either through regiment training, horde battling, simple battling or if person did so powersave hacks n forth.
also a Pokemon at lv 1 with desireable moves and ivs or whatever your running whatever it is then if battling in battle spots its level goes to 50 anyway also its ev's would be lower than a Pokemon at lv 100 simply cause battle spot works at lv 50s however it all gets evened out
if battling on lv 100 Pokemon then the adjustment is made because of higher levels it automatically gets done for you and ev's stay same as in input but stats change..