Thanks Sireland. That backside looks blotchy to me. I guess I'm not too concerned because it'll never be seen. The camera tends to 'wash' a lot of details so it's difficult to see all of the grain pattern in the photos.
I started applying the third coat on the backside this afternoon. It'd be great to be able to do the fronts and backs at the same time but I don't know how I'd ever be able to do it without the saw horses messing up the finish. I thought about leaning the boards against a wall but I was afraid that I'd risk getting runs in the varnish.
The wood is still sucking that varnish into it. I'm starting to see a slight sheen to the finish but these side boards are way more absorbent than the floor boards were.