Yeah, purity I suppose, but in my experience most peas don't naturally cross all that much. Now when you try to grow a lot of peas like 17+ varieties all with colorful flowers in close proximity the cross pollination rate may increase quite a bit.
Mostly it's for some I have very little seed for anyway. Like one line that is super rare and has black seeds. Or a few from Ethiopia or 1 line of pisum fulvum which may cross with domestic peas with or without genetic difficulties. Etc.
If I haven't already, i can send you some NAP gene seeds. I got plenty of seed to share from that last year. But the one line of cochleata I only have enough to send maybe 1 person. It might be worth requesting a few other coch lines as well as they might all be different.
Diane, where are you located, when does your season start, and how many varieties could you fit in?