http://api.twitter.com/1/help/configuration.json has a list of non_username_paths that can be used to tell if a URL on twitter.com/ belongs to a user or not. twitter.com/500 and twitter.com/503 are non user URLs, but don't show up on that list.
Would be nice if either the /HTTPCode URLs either went to a user or showed up in the non_username_paths list.
Updates
- We'll consider the successful resolution of this ticket either the screen_names being added to the non_username_paths collection OR the ability for usernames that correspond to error codes to be accessible via twitter.com/screen_name