Yeah, Svalbard and Jan Mayen doesn't have any official flag except from the Norwegian flag. The flag used is a proposed flag of Svalbard from 1930.
Same for the flag use for Saint Martin. It's also an unofficial flag and the only flag for the Collectivity is the French flag. Although the government has a local flag
The site you refer to calls that Saint Martin flag dubious and says no one on the island has ever seen that flag, so it may be a stretch to include it in the quiz. The rest of the quiz is great but including unused flags and proposals like the Svalbard one is, I think, asking for a bit much of the player. Also, maybe accept answers without having to type out "island" every time? Fun quiz regardless though :)
Same for the flag use for Saint Martin. It's also an unofficial flag and the only flag for the Collectivity is the French flag. Although the government has a local flag