I've been reading a bunch of info that is saying the old hermie's produce hermie's belief is not true and that it's a normal expression. Some strains just do it easier than others due to stress, age, etc.
I've got feminized hermie seeds I've been hesitant to grow but might give them a shot. I've definitely learned another reason for growing single strains, or at least strains that finish at the same time. Most of my worries would be gone of I didn't have other plants still with weeks to go in the same room.
There are definitely some genetic lines out there that seem to love herming and I avoid those, but in all of my many years of growing have i have never seen a stable line become hermie prone just because you stressed a plant and it chucked nanners.
The strain I just had self on me has always been great and up until this run I only had nanners appear once. That was due to being out of town several weeks during late flower and not being there to correct a major pH problem in my reservoir. Got 4 or 5 viable seeds out of that plant and have since grown them all. They all behaved themselves just fine.
Basically, if you give a plant an optimal environment and it still throws nanners on you you should be wary of those genetics, but if you know it is from grower errors like severe over/under feeding, over/under watering, timer failure/serious light leaks, or major temperature issues, you most likely don't have to fear using the resulting seeds.