I think that we need to set some guidelines on which unidentified individuals merit having their own articles. As I general rule, I think that there should be some information on the character available (e.g., their job, their relationship with another character, something they said or did), in order to give the article a solid foundation.
I don't think we should have articles on characters whose existence can only be inferred. For example, it's a given that Lucius Malfoy had a mother, but I don't think she warrants her own article, as she is never mentioned anywhere in the series, unlike Lucius' father Abraxas.
Also, although JKR has said she created forty students in Harry's year, I don't think we need to have articles like "Unidentified Slytherin girl," simply because it can be mathematically inferred that there was a fifth girl who shared a dorm with Pansy, Millicent, Daphne, and Tracey. We already have articles on all the students whose names appeared on the list in Harry Potter and Me, including ones whose Houses are unknown, like L. Moon, Sally-Anne Perks, and Malone. The missing Slytherin girl is surely to be found among these names and thus the "Unidentified Slytherin girl" article is kind of redundant. However, I think the two unidentified Gryffindor girls warrant their own article, because JKR has mentioned them on three occasions,[1][2][3] giving us a more solid foundation to build upon than speculation.
I also think we need to be more selective when it comes to creating articles on characters from the films. Simply appearing in a Harry Potter film doesn't seem a strong enough basis for a character having an article, because hundreds of extras have appeared in the films, and having articles on all of those characters would be excessive. ★ Starstuff (Owl me!) 11:02, September 28, 2009 (UTC)