Considering what "mess" they did with all the saber versions I think they had some droid callers in a box and on the set: "Hey the droid caller is missing on your belt. Go to the droid caller box and take one." :lol
Sounds like something that could happened back than. We only have such problems with different versions because of the internet. Without nobody would compare every picture that is out there.
For example: I haven't seen a picture with a hole in the dome yet :wacko
Yes,...it really does.:lolIve seen it all three ways. Im a dome topped guy myself. Wait, that sounds kinds weird....
http://i833.photobucket.com/albums/zz258/Sym-Cha/Luke ANH Droidcaller-01_zps3a6f5rdy.jpg
Seems a dome has been attached in this vintage picture :wacko