After publishing the initial video about this project on YouTube, I inspected each of the eleven PCBs with a USB microscope. Here's the amount of soldermask misalignment I found:

So I've got eight usable PCBs and three that I could use in a pinch.

I also had a couple of recent OSHPark PCBs, so I decided to check them. Misalignment on those was about 0.5 mils or less. It would have been nice to have that tight registration, but they don't offer the 4 mil trace/space and 8 mil drills that I needed.