It really depends on whether they intended it for a potential theatrical release or not. 90’s theatrical releases had two surround channels. Running even the 77 4 channel mix through a pro-logic decoder produces unique left and right surround even though we know that was not what they encoded. So what I’m seeing comparing the different mixes could be a decoding error, but other than adding in a few of the mono mix edits to ANH, making the mix with stereo surround seems like the most logical reason to make a new audio mix for all three films.