Lucas was remixing the movie while it was already released in 1977 so I guess 1981 might be different. Was the mix redone in 1985 ? (with the C3PO line added on the DS ?)
There were three mixes in 1977 (35mm mono, 35mm stereo, and 70mm six-track). These were the only mixes used until the 1985 stereo remix. The 1981 ANH theatrical reissues all used the 1977 stereo mix (I think; it’s possible some used the mono mix, but as no 35mm mono was prepared for ESB, I doubt it).
The mix you’re thinking of is the 1985 remix.
Almost all of the 1981 ANH reissue prints were just 1977 prints with the opening logos, crawl, and flyover chopped off and replaced with the 1981 version.