Yeah you have to complete at least 90% of the nodes for it to be marked as complete. If you search the forum for “hard mode”, you’ll find a conversation around the idea of requiring 100%.
This post: Overpass Street Query has a link to the sheet that describes my OSM query. It’s basically a search for all “highway” records, with a list of records to ignore (private roads etc). That might help you figure out why some streets aren’t in CityStrides.