Figured it was worth throwing my $0.02 into this because I'm a statistical nerd and all.
If we're talking about AIC, then they made several things before Tenchi Muyo!. To save you all a trip to Wikipedia, Bastard!!, Bubblegum Crisis, Burn Up!, Dangaioh, Detonator Orgun, Fight! Iczer One, Hades Project Zeorymer, Megazone 23, and Vampire Princess Miyu are all listed as their first episodes having been released before Tenchi OVA 1's first episode. And that's just counting a few of the OVAs, not one-shots, TV series, or movies. Also, AIC has been around since 1982, not 1992. So this year would be AIC's 40th anniversary (Albeit this year is, as has already been mentioned here by several people including myself, Tenchi's 30th). The Wikipedia article I referenced has lists of AIC's works (One each for TV shows, OVAs, and movies) that all come with a handy option to sort everything by first run start date so that you can piece everything together.
Now, if we're talking about anything that specifically falls under the Pioneer / Geneon / Universal banner, then yeah... that's something that Wikipedia isn't being a big help with. All my brain is registering from their article is that they mostly produced and distributed the laserdiscs, home videos, and so forth, but didn't actually make the shows, OVAs, etc. themselves. As such, that is a discussion I can't really jump into because I'd be as good as that annoying buzzing gnat flying around the discussion table because I wouldn't be able to contribute.
TLDR I can confirm that Tenchi isn't AIC's first work specifically, but I can't vouch for which of AIC's works would be the first to fall under the Pioneer / Geneon / Universal banner, because that I legitimately have no clue about, LOL.
