cherry pollination is a little more complicated than most other fruits.
There are different allele’s that cause self infertility. Those are named S3, S4 etc
Each tree has a Pair. Like S4S5 for example. And can’t set fruit when pollinated from S4 or S5 pollen.
However if you plant a S3S4 tree near for example an S4S5 tree. Half the pollen will have the S3 allele and the other half the S4 allele. Since pollen only carry half the genetic code of the parent. And thus half the pollen can fertilize the tree.
The S3S4 tree can set fruit from the S5 pollen. And the S4S5 tree can set fruit from the S3 pollen. This usually is enough for a good fruit load.
However they irradiated some cherry’s till the S4 allele broke. And it thus no longer fulfils it’s function of avoiding self fertilization. We denote the “broken” S allele’s with an ’ like S4’ for example.
So not all S4Sx cherries are self fertile. But all S4’Sx are. Same for cherries containing S3’ and S5’ although there seem to be way less of those.
it is explained in part in this document. that i posted before.
page 30 lists universal donor’s. Those have and unique S allele combination. That no other variety has (maybe future Varity will have)
And thus if you plant 2 cherries that flower around the same time. And 1 variety is of page 30, both can be successfully pollinated.
for example Antuono S10S16 is such an universal donor. There are other cherry variety’s with S10 and others with S16. But none (yet) with both. So if you pick any other cherry, at least half the pollen will be compatible.
Then page 31 and 32 list the self compatible cherries. Those have a “broken” S allele. And thus the S allele no longer blocks self fertilization.
in this topic. i posted a few other links about cherry S allele. You’ll have to buy the articles or use sci-hub or an university library to read them though. There it is explained a little bit more elaborately.
however since your tree’s had some cherries. I think pollen incompatibility is likely not your problem. It might be poor pollination due to whether or lack of pollinators. (although it could have been that your tree’s are the same S combination, and you got lucky once from an insect coming from another cherry tree far away