Spent some more time this afternoon and put red dots on rear spar holes that should not be riveted until later (as per the instructions).

I only put the red dots on the holes that I would be tempted to rivet (because I'm riveting a rib or assembling the rear spar), not every single hole that shouldn't be.

The rear skin support channel (I think that's what it's called) doesn't go on until all the ribs are riveted in place.