Fundamentally, the game behaves the same between both SNES and GBA versions in regards to stat math.
However, there is one minor difference.
In FF4, for any stat the goes below 0 (Cursed Ring can make this happen), will be calculated as 1. The exception is that the stat can be 0 if the stat additions+losses equal 0.
In FF4A, for any stat that goes below 0, the game will display 0 for that stat. However, internally, the value is still negative when doing the stat calculations. There is probably a lower limit where a stat can be negative. For instance, if you manage to have negative vitality, the lowest defense rating you could get is 0, and not a negative number.
We have EVEN MORE themes now, but some old ones are gone...