Well, the thing is that there are three preserved aircraft of which I have a second photo, shot on the same day, in the database. I don't think these were accepted in error, so it seems to be acceptable sometimes. Admittedly, in these cases the difference in angle was greater.
When I started editing this Il-28 shot I didn't realize that it was the same a/c I already had in the db. I'm happy to pull it if it's felt to be against the rules or even the ethics of the site, but I could do with some clarification.