My presumption would be that it one would have to match the variation you are after, e.g. an ANH blaster if you're doing the sideshow figure variant, or an ROTJ blaster if you're doing base ROTJ armor. This is actually what is captured in the current EIB standards.
What do you guys think? Or should we allow any EIB version blaster version as the details aren't really captured in the screen caps, and what one can see doesn't match anything from the movies, most especially the barrel, and w/o solid references we shouldn't strive to be that anal the first go-round.