This topic actually made me register here. Great work everybody ! And sorry to bring back this conversation, hope it won't be considered bad manners ^^
I consider myself a fan and a collector of LBG (and other Dez/Daei shows, but less so) stuff, with video releases among them, being somewhat in pursuit of a non-existent 'perfect' release. As far as I know, the japanese 'eien no miko mido' LD-Box is the only video release to feature the missing classroom scene in episode 6. There may be also a doubt about the very first US VHS release, but as this version still eludes me, I can't confirm it.
In fact, production of episode 6 was somewhat chaotic, with bits of the script modified at the last instant, and several scenes didn't did it to the final cut. It was restored in the collector LD-box, but the status of this bit of animation seems to remain somehow a little vague. It don't help that the rights has changed hands since then : DEZ was an adult video label created by Daei at a times when part of the capital of Daei was owned by Tokuma - which explain the japanese DVD release at the beginning of the 2000s : the company which gave birth to Ghibli seem to hold the rights for Japan, but don't seem to care about the title... so the bit of animation (which wasn't included in the japanese DVD) may still exists in Studio Kikan/Arms vault, but may be lost in japanese licensor hell.
Well, I said the scene wasn't included in any video release I know of, excepted for the LD-Box. There is another exception : japanese multimedia cdroms. You know, the kind with clips and images. You can find this scene on one of them, badly encoded indeed but it's better than nothing... does it interests someone here ? And others censored clips from the japanese DVD as well ?
And somebody (elgringo14 I believe ?) mentionned old Yamato VHS in relation with this other great classic butchered by occental editors, Twin Angels. Just to be coplete, I wanted to mention that Yamato VHS release of La Blue Girl is also unedited/uncensored (yet again, excepted for episode 6). Copies still float around on Ebay.it, if you are interested enough to hear the characters speak in italian.