I was wondering if anyone had photos of plums that grew from rootstock? (not grafted plums on a rootstock)

I am beginning to suspect that at least one maybe two of the old plum trees we have are actually root suckers.

I have new Mariposa and a grafted plum/peach test tree with a variety of scions that took. The two suspect trees are done for the season, first is a small yellow/yellow (blooms white) that ripens late May/Early June-this one seems to root pits like mad-I have to pull baby seedlings out regularly. Second might be a methley, but am thinking it is likely rootstock. Blooms white is red/red for the fruit (Red outside/red inside) And it seems to spread by rootsuckers and is also pretty much done for the season

Both have much smaller fruit (1-1.5") no matter the water.

Any thoughts?

thanks