Please help. I recently sanded my hardwood floors, they are red oak, but had a light yellow finish to them. I went through the progressions with the U-Sand, 36-24-40-80-120, trying to make sure I removed all the finish. Sanded out well. Stained with Minwax Early American. Dining area looks great. However, in the living room, it seems like the stain withdrew from the edges of some of the boards, and the lighter wood (maybe partial finish?) is showing through. I touched it up with a brush, but it still doesn't want to absorb. I even hand sanded a small patch (120 grit) and stained again, but it still sticks out like a sore thumb. Any suggestions?

You are probably correct about not getting all the finish off the edges. You may also end upp with problems with the finish adhering to those areas. Probably needs to be resanded. Might need to go with a more agressive sander to get the finish off and then if you want switch to th u sand.

use a scraper..remove the excess color and the old remaining finish.
then take a piece of 50 grit paper...rub those areas..
touch up stain..let stain tack a little,then remove all excess..should blend right in...

if u fix it before u put any finishes on...it will be no issue