The fourth Mix did not come about til 1985 and not 1981. It was a digital mix and i believe the tractor beam line by c-3p0 was added back in. The remix was stereo not mono. Only a single mono mix was ever made for star wars and would have been heard in 77-78 during its original run.

IMDB is not the best source always for infromation as like wiki they can have random people add info that is not fact checked.

IMDB own sources are often accurate to a certain degree. I have found them to sometimes have stated inaccuracies about a film just like any information database is subject to human error.

Not sure if the 1985 mix has close the blast doors. I know the blast it wedge is only in the mono mix and blast it biggs is in every other version.

I know the Tractor beam Line was left out of the 1993 Definitive Collection MIX, and the close the blast doors open the blast doors was restored in the 1997 special edition mix.

Star Wars had 3 mixes in 1977. one in 1985, another in 1993. another in 1997 and 2004. Seven sound mixes begins to get a little rediculous. Besides the fact that only takes into account the ones in english. I have no idea how many foreign dubs have been made for star wars since 1977.

The least complete mix in 77 was the six track. the Most complete was the mono mix and was at the time considered the definitive mix.