I have two dogs. One's recall is very good. The other ones is so so. If he's off lead, I could get him not to approach another dog as long as it's a fair distance away. He would stand, look at the dog but not come back and I have to fetch him. If the other dog is quite close then I have difficulty recalling him. He'll be off wanting to play. He thinks every dog wants to play. Not ideal as you don't always know what the other dog/person is like. Tried recall training at home and in quiet park, been successful but when real situation arises it's not reliant.
Total Recall by Pippa Mattinson is very good. You have to put in some legwork but it's worth it. Mine wouldn't ever come away from a dog before, but is pretty much 100% now. Even on the odd occasion she doesn't come immediately to the whistle, it is only ever thirty seconds or so later.
The squirrels still trump the recall to whistle, but we work around that!