I'll try to make a long story short. I'm sanding my hallway floor to re-do a refinishing job that I messed up (polyurethane). Using a 21" belt sander with 50 grit I've taken it mostly back down to bare wood. Do I need to remove ALL of the finish or can it be less then perfect since I will be re-applying the exact same finish?

If you have just a little bit of finish after 80 and 100 grit sanding it won't show up if you use the same finish and apply two coats for finishing.

thank you