Did ATK determine max backstab damage on live?
 

I'm almost positive it did so in later expansions which is why people stacked ATK items, was it supposed to back during classic?

Also does it effect white damage on p99? It for sure doesn't change max BS damage.

I always thought that it modified how well your attack stacked up again the mob's Armor, so having high ATK would give you a better chance to hit for a higher amount of your weapon's max, but it would not actually change the maximum dmg/swing your weapon could do.

Same... I believe STR is the only way to increase your max damage from any attack, but having higher attack was a way to have a better chance at hitting/have a better chance at hitting for more as such:

ATK vs AC/AGI check - determines hit chance/hit damage
STR can add damage over base + bonus damage

^ this
and you mentioned white damage, WoW player! GET EM!