Earlier in the thread, the discussion of when/why there was a change (definitely credits, maybe crawl), sometime in the first year or two after release. Here's an idea for a why.
http://adayinhollywood.tumblr.com/post/16928556714/august-3-1977-the-second-opening-of-star-wars
1977.08.03 is when they put 3po, R2 and Vader's feet into the sidewalk in front of Grauman's Chinese Theater. The above link considers this the second opening of SW at the Grauman. As this was a special day they probably wanted a perfect print for the showing. Why not use this as a possible start date for all newly printed versions to have slight updates.
This date would also make a good transition point as it coincides close to the beginning of the international release schedule. Which began 1977.08.23 in the Philippines, according to:
http://www.imdb.com/title/tt0076759/releaseinfo
So if August 77 is the cut off date, there could be 843 prints of this early version out in circulation at some point:
http://boxofficemojo.com/movies/?page=weekend&id=starwars4.htm
But as they were just lopping off the beginning and end of the film, this date could be shifted up a few weeks. If someone knows how long it took to produce a print, subtract that from the August deadline. If it is as much as a month, then that would almost cut in half the number of original version prints. ~453