seedling plums

seedling plums. sort of prunus americana but a little larger, darker, the skin is a little better, they ripened a bit later. is it a wild plum? sort of I think, it's like a gradient, these might be 75% american wild plum, it's a guess. starting to find more of these trees to collect from, I think the right category is just seedling plum. thinking I should just mix them together?