Draw Bound Area Problem

I receive plans like the attached from my clients. I always have problems when I try to hatch the North point. When I use Draw/Bound Area, I can change the arrow into a polyline, which I can then hatch. However, when I do the same on the N it says "boundary not found". The only way I have found round this is to draw over it with a new polyline, but this is very time consuming when I have to do it 20 or 30 times a day! Can you help?