If you output
GetLFGDungeonInfo alongside the boss names and compare it to the HFC page on wowhead you'll notice Blizzard's idea of what order the 13 bosses are in doesn't match.
The function inexplicably doesn't return valid information for bosses outside of the wing despite listing all 13 of them, so you'll have to make sure you have the right dungeon ID for the right boss number.
Here's an example that's kind of pushing the macro limit, but should output the bosses in the correct order with valid data.
Lua Code:
/run for i,v in pairs({{982,1},{982,2},{982,3},{983,5},{983,4},{983,6},{984,7},{984,8},{984,11},{985,9},{985,10},{985,12},{986,13}})do local n,_,x=GetLFGDungeonEncounterInfo(v[1],v[2])print(GetLFGDungeonInfo(v[1])..':',n,(x and''or'Not ')..'Completed')end