In the case of Cy Town, he was an extra, most likely during the Emperor's Arrival/Vader's Arrival scene in ROTJ. As far as his career is concerned, ROTJ was barely a blip on the radar. On the other hand, he was a Dalek operator on Doctor Who for years. While is is happy to sign for fans, he is very frustrated by being bombarded with SW mail, and would like to be disassociated with it altogether. This is something he makes note of every time he signs a ttm request. As such, he won't talk about it because he doesn't want to fan the fires, so to speak. It's a pretty safe bet he was on the set as a trooper or officer, and he doesn't want to advertise it.