All levels exept 8-4 are limited by the framerule system of the game so it's not really useful that each level has his own IL category. You can be the faster in a level but there will always 0.35s gaps. 8-4 IL category exists (https://www.speedrun.com/smbce#8-4_IL) because the time is counted frame by frame on the axe.

Oh well it's SMB Special, there's no 8-4 IL category lol