Berserker Island is missing from Hiccup's map.

Hiccup's map doesn't have Berserker Island or Defender's of the Wing Island. Berk had a treaty with the Berserkers way before RTTE. And Dagur was clearly able to find Berk, so Berk was on his maps. Why not Hiccup's map? His map has WIngmaiden Island, Melody Island, Dragon's Edge, Outcast Island, Storehouse Island, Dark Deep, Isle of Night, but no Defender's of the Wing Island or Berserker Island.