Yeah the period between years 1986 and 1994 was really poor in terms of explicit titles, especially if you compare what has been done since 1994 and the beginning of Pink Pineapple productions.
In 1989 started the "Otaku murderer" affair (
http://en.wikipedia.org/wiki/Tsutomu_Miyazaki) and this meant that most companies kept a low profile for the years after concerning explicit anime material.
If I take the period 1990-1993 as you mentioned it, I can still find a bunch of titles:
CENSORED
David no Hoshi (5 episodes, no subs) which is a wrecktrain story of someone obsessed with torturing pretty girls, but the animation is really bad
Sexy Animerama (4 episodes, no subs), a mix of Idol live action and explicit adult anime, not that exciting
Lyon Flare (2 episodes, commercial release) episode 1 from 1986 and episode 2 from 1990, episode 2 has still one mosaic
Adventure Kid (3 episodes, commercial release) episodes 1 and 2 are still censored, and episode 3 is not explicit
Angel (1 episode, fansub by Erobeat) the original OVA was rather explicit, not to be confused with 'Shin Angel'
Telekura no Himitsu (2 episodes, no subs) some strange semi-documentary story about telephone clubs in Japan
The Urotsukidoji sequels:
Urotsukidoji Matai Den or 'Legend of the Demon Womb' (2 episodes, commercial release)
Urotsukidoji Mirai hen or 'Return of the Overfiend' (4 episodes, commercial release without subs, fansub by Hentai-Palace)
Urotsukidoji Houhou hen or 'Inferno Road' (3 episodes, commercial release without subs, fansub by Hentai-Palace)
Only the movie edition of 'Demon Womb' has no censorship, but no subs, otherwise they all have censorship as color dots.
I also have to mention Cream Lemon, as some episodes were released in the period 1990-1993 (6 episodes are concerned, none of them subbed yet)
UNCENSORED
Guy (2 episodes, commercial release) ep 1 from 1988, ep 2 from 1992, though ep 2 has nothing explicit
Ogenki Clinic (3 episodes, commercial release) some scenes are rather explicit, only episode 3 exists with subs though
The Daiei productions:
Youjuu Kyoushitsu/Demon Beast (6 episodes, commercial release)
Inju Gakuen/La Blue Girl (6 episodes, commercial release) the current version has many edits
In principle you can find all the titles which weren't licensed in this forum. :study: