Hey clay_c, I don't remember exactly... but, my best guess was that I used both the EIS (which showed completed sections of the tunnel box) and the photo. The EIS was showing slightly further construction different than the photo, and I think I approximated the ends to account for uncertainty?
If you did see imagery years ago, and the photo backed up what you saw, you've got ground truth on your side; feel free to correct my mistake (I'm not sure how to do it myself)