The flags for the following countries are missing (HTTP 404): San Marino (SM), Liechtenstein (LI), Equatorial Guinea (GQ).
Hong Kong is considered its own flag, which makes sense, but then shouldn't Macao, which has almost the exact same status within China (Special Administrative Region), also have its own flag? Both flags exist as emojis
Currently, I've you been to Macao, it shows the PRC flag. Imho, that's like saying you've seen Denmark, when you've been to the Faroe islands.
The same logic is also applied for the Dutch Caribbean islands (Curacao or Aruba for example have their own flags). It seems just Macao is the odd one out.
A similar argument could be used for Gibraltar.
If you go strictly by what's available as emojis, then e.g. the Canary Islands also have their own but are not counted extra on nomadlist.