This is great work!
Recommendations
1. mirror the tDocu (51) layer to bDocu (52)

- tDocu (51) mirrored to bDocu (52)
- Screen Shot 2018-01-05 at 10.25.42 AM.png (335.33 KiB) Viewed 18812 times
2. 2x20 header... ...square via the correct end

- square via on bottom right of header
- Screen Shot 2018-01-05 at 10.28.46 AM.png (97.54 KiB) Viewed 18812 times
3. PP5 isn't used by most Gameboy Zero builds, you can get rid of it

- PP5 removed
- Screen Shot 2018-01-05 at 10.54.56 AM.png (330.12 KiB) Viewed 18810 times
4. You can additionally get rid of the HDMI test points (39,36,20)
5. Labels are nice

Drill holes are removed as this will impact your design as well

- Screen Shot 2018-01-05 at 11.11.00 AM.png (249.8 KiB) Viewed 18809 times
Reference

- reference
- Raspberry-Pi-Zero-Back.jpg (356.49 KiB) Viewed 18812 times