It's easy to tell. When you spray through the injector while cleaning, it atomizes the brake cleaner. If one or all the holes were clogged, you would...
Yep! Worked every time for me. There is a video somewhere in youtube with a demonstration. It takes a bit of practice and needs to be done outdoors....
Try it, you'll see how disorienting it can be to not only describe a process but to record it & keep the relevant parts in the frame of view. Unless...