This is one the many reasons I like 2nd ed better. -10 AC is the limit you can't go any lower. (I know ToB did and they shouldn't have)
Interesting that typed AC, e.g. vs Crushing, vs Slashing was unlimited so could go below -24 limit in the BG1 and 2 engine, so you could drink stacking Potions of Absorption (-10 bonus vs crushing) to have unlimited ac vs crushing.
