The parts for the Unicorn circuit board arrived! The circuit boards themselves sill aren't here, of course (cheap shipping from China is cheap and slow). Anyway, I went through the parts I received and, lo and behold, I got one wrong. Thankfully, it was only the switch—I had ordered a surface-mount version instead of a through-hole version. The good news is I can still use the switch. I have corrected the part number and price in the part list spreadsheet.
On a slightly related subject, I finally assembled the Magnetic Rotary Encoder board!
It's pretty cool. The surface-mount soldering, while not impossible, is still a pain in the butt. Also, getting the rosin flux off the board was fairly difficult, too. I feel like Hackaday did a how-to for using flux, but I can't find the post right now. If any of you has a good method or a link to a good method of removing rosin flux, leave a comment.