I.ve found most C.Pubescens like lower germination temps. -mid. to high 70's.
Lower than that and they mold or whatever,higher they cook...
I don't have a problem with germination of fresh seeds but do find they like to hold their shells at time.
Also scratching the seeds or removing stuck shells ,for me,causes more damage than good.
Cracked shells expand fast but the embryo comes out of the shell and usually molds or whatever.
Stuck shells that die are from weak plants.
If they can't grow their way out of the shell by themselves ,you have a weak start that isn't worth messing with in my opinion.
It'll need constant attention until it grows big enough to get it's act together...
But I might consider pulling a shell off if it was the last seed for a VERY VERY RARE strain.Probably not...
Then again,I have several LBS. of Manzano seeds...
I mostly only buy 3 1/2 inch + sized manzanos for my seed stock(google Dino Pods,Peru Baseball).