Actually, I've had nearly 100% success propagating Mexican/equatorial Pinguicula, from leaf-pullings. It never really mattered as to what leaf form the plants were in, at the time I took the pullings. I've propagated many hundreds, perhaps thousands, of plantlets from both summer and winter leaf forms. The most important factor, is to control the moisture/humidity in the immediate vicinity of the severed leaves. Too damp and they will quickly rot, before forming plantlets, too dry and they will dry up, before forming plantlets. Besides, many of these are homophyllous, and only ever have "summer" leaves.