On May 25th of 1977 Star Wars opened on only 32 screens. Of course of the 32 prints made for opening day 8 of those prints were in 70mm. Now you have two versions. There were 24 35mm and only 8 70mm versions. So the alleged missing footage could just be missing out of 8 prints or the 24 35mm prints. Now take into account the various sound options on the two prints. You have Dolby, Mono, and 70mm Dolby. Dolby opened on 12 screens, Mono opened on 12 screens, and the 70mm Dolby opened on the other 8 screens. So now we have three separate versions of the opening day Star Wars of which the footage could be missing. Two separate versions of the 35mm and the 70mm. The footage could be missing out of the 12 Mono prints, the 8 70mm prints, or the 12 Dolby prints. It's no wonder some say it was missing and some say it wasn't. Hell it could just be missing on only 8 prints EVER. That would be reason enough for something to pass into myth.

I guess we'll have to invent a time machine and go back and see an opening day print to be sure because you’re right, I can’t prove it; at least not without a doubt anyway. But that is my case for the possibility of the fact that the two scenes very well could have been missing from the opening day version of the movie. I can’t prove it right but you can’t say that there is no way that of all the versions of Star Wars that has been put into theatres that it’s impossible for two scenes to be missing out of 32 (Or even less) prints.

Here is a great link to info about Star Wars opening day. It doesn't have info on the (Possible) missing footage but it's a great read none the less.

http://www.in70mm.com/news/2003/star_wars/star_wars_1977.htm