Any explanations as to why...

[Pickle Girl Fanboy]

... the Espers look different in FFT and FFXII?  Is it canon, or graphical limitations?

[Archael]

creative liberty

[Shade]

caus the creators of XII suck balls.

[Eternal]

I think it's more or less because the creators didn't have a solid design for them in mind yet. So when they were making FFXII, they decided to add in things that they thought would be cool that came after FFT.

[Pickle Girl Fanboy]

If it's not canon, then no one will shit a brick if you reinterpret the FFXII-only espers when spriting them for FFT?  Because I like the FFT espers better than the FFXII ones, except maybe for Ultima.

[Kaijyuu]

Small details like these can vary between artists, and really no one cares. Do whatever you want.