The movie was significantly changed in the Special Edition version of Star Wars in 1998 in the run up to the first prequel movie Star Wars Episode I The Phantom Menace in 1999.
This was a very rare treat for fans of the series as the Special Editions, especially of this movie, have caused controversy over the year, especially the now famous "Han Shoots First" scene.
A brief history of this print of the film as found in various sources on the internet:
The BFI (British Film Institute) found the print in their archives and after contacting Lucasfilm about doing a screening they agreed.
Lucasfilm president Kathleen Kennedy said she was surprise that the print existed, but agreed to the screening as she thinks it is a valuable artifact in historical cinema.
Kennedy presented the showing to prove it was a legal copy!
As explained by the BFI
"In these very special screenings, we present the film exactly as experienced by audiences on its original 1977 release. Screening from one of the precious handful of dye transfer IB Technicolor prints produced uniquely for the first British release, and preserved in the BFI National Archive"
Lets hope this sentiment to the original cut goes that bit further and, as the whole trilogy is owned by Disney since the buyout of Fox, it gets a 4K remastered home release, as well as Star Wars The Empire Strikes Back and Star Wars Return of the Jedi.
More in fo can be found here.