Thank you for writing.

Here is an atlas of plum diseases.

https://www.gardenfocused.co.uk/fruitarticles/plums/pest-disease.php

The good news is that this is not curcullio. 

To my eye the difference is aphids or plum aphids v Japanese beetles.

Japanese beetles love plum trees and can do this kind of damage BUT they are easily visible.

Aphids get the munchies near plums but they curl the leaves.  https://www.gardeningknowhow.com/edible/fruits/plum/control-leaf-curl-plum-aphids.htm

Your lesions look like shot hole disease, common on plums, http://ipm.ucanr.edu/PMG/GARDEN/FRUIT/DISEASE/shothole.html#:~:text=Shot%20hole%2C%20or%20Coryneum%20blight,hole%20disease%20affects%20Prunus%20spp.&text=The%20disease%20will%20develop%20on,weather%20during%20winter%20and%20spring.

https://www.farmforum.net/farm_forum_columnists/tree-facts-shot-hole-disease-of-trees-and-shrubs-in-the-plum-family/article_a31f28c8-6aad-5bd9-bbad-f244276b9c06.html?redir=0

The management for shot hole is a bit specialized.  If you do not see Japanese beetles, I suggest that you consult with a certified arborist to help assess and manage this condition.  https://extension.umn.edu/planting-and-growing-guides/how-hire-tree-care-professional