One room in my house has been occupied for the last ten years by a very
heavy smoker, so I'm redecorating it.

The walls are coming up fine with a hard scrubbing and a repaint, but
I'm not sure what to do about the woodwork, which was painted ten years
ago with white gloss.

It's all in very good condition -- no flaking, very few dents and chips
etc -- and in other conditions, I would be happy to just sand it with
wet-and-dry, touch up the chipped bits, and then paint one undercoat
before re-glossing.

However, the normal sanding doesn't entirely remove the yellow stain. I
don't think I need worry about it showing through the paint, but I do
worry about it not providing enough adhesion.

Can anyone tell me whether I need to sand off all the yellowed stuff?

Thanks!