Accessing profile photos


I’m trying to access Twitter users’ profile pictures but am using some data collected before the image hosting domain change. I’ve noticed that some profile photos are accessible when I change the URL from “http://a0” to “http://pbs,” but that the photo I access doesn’t always match the photo that the user currently has posted. When this happens am I just accessing archived photos from that user, or by changing the URL do I run the risk of accessing a completely different user’s profile photo?