What a shame that these mature dogwoods are so infected! There's a good chance that it is dogwood anthracnose, which our native dogwoods are, unfortunately, quite susceptible to. However the leaf damage doesn't quite follow the classic anthracnose pattern, so it could be a different leaf-spotting fungus.
Would you check the twigs and branches of infected leaves, and look for any canker-like blotches or sunken areas? Are any of the branches dying back?
Also inspect the underside of infected leaves for any dots or specks that could be a source of spores. Send pictures if you can.
Do you recall if there was any spotting or dieback of the flowers? Has this appeared in previous years?
Here are a few references:
https://pnwhandbooks.org/plantdisease/host-disease/dogwood-cornus-spp-anthracnose
https://pnwhandbooks.org/plantdisease/host-disease/dogwood-cornus-spp-leaf-spots
https://extension.umd.edu/resource/dogwood-anthracnose/