Brendan I’m the same. And it’s actually one of the best ways to improve. I think your progress has been remarkable since I noticed you posting on here, and I’m sure it’s in no small part due to that.
If I’m right about the “extra mark” idea it is devious. The concept of altering letters, eg remove a loop to go from B to P, occurs every now and again and almost always catches me out. So I probably see it when it isn’t there!