HelIconoid butterflies. I am sorry. Typo. Heliconoid = "like a Heliconia".

Ah, yes, I know Passiflora ligularis. Never tasted it though.
Yes, Passionflower seed has short longevity. However, all is not lost. Fresh seed germinates quickly, but stale seed isn't necessarily dead; it tends to go into a deeper dormancy, that is harder to break.
BTW, you almost certainly already know that it takes two Passionvines to make fruit. They are self-sterile.
Passionflowers cross readily, but being an ancient breed, they don't always, and sometimes the hybrid offspring are themselves sterile. Try to stay within the same subgenus. P. mollisima is a Tacsonia; it crosses well with other Tacsonias--and it is one of the easier ones to grow. It is coldhardy BRIEFLY down to about -5C.
The only Passionflower common here is P. caerulea, the Bluecrown Passionflower, from southern Brazil, that is strangely coldhardy (down around -15C or so) and rampant. One reason it is so coldhardy is that it suckers readily from the roots. Unfortunately, it has some of the poorest fruit of the genus.