Seen, say, in Darwin the bird might be a Pin-tailed Snipe (G. stenura) or Swinhoe's Snipe (G. megala). How to tell the difference? Easy. Catch the bird. Carefully count the tail feathers. Got 18 or fewer? It's Latham's. Got 20+? Pin-tailed. Got 24+? Swinhoe's.
See? Dead easy. Do you know, there are some people who say bird ID can be difficult!