Now I can confirm it is impossible for at least Pteras...
I just got mine to 97% imprint, while maturation progress is at around 90%. Next imprint in 3.5 hours, when it will already be grown up.
By the way, is it still possible to get 100% imprint now?
I got 32% on a Ptera at about 30% maturation progress, which means 64% at 60%, 96% at 90%, 96% at 100% maturation, no?