as anyone can see from the Notan series cover illustrations above which were released around 1995- 1996 OVA 3 was always meant to be preceded by these prequel stories. infact OVA 3 makes very little sense without them and this is often why so many people in the west are lost when they first watch OVA 3.
From the end word of the last volume we know that in fact these stories went through various attempts to release them in different formats such as audio dramas and based off of their structure it's easy to see that they were meant to be done as films or rather film length OVA's
But what if these are why OVA 3 was delayed until 2003?
There are many rumours as to what happened. some say kajishima was told that he had to make AIC a few shows before he was allowed to continue the OVA and thus dual and GXP were made... I don't buy that.
Aic split from pioneer if i remember correctly and we know they cut OVA 2 short because of it.
there is a storyboard showing Tenchi's mom approaching Tenchi at the end of episode 13 that got cut in the aic sketchbooks.
When split they wanted to establish themselves so they needed a good series to start with... so they passed on the true tenchi's and started by making Tenchi universe a commercially viable vanilla version of tenchi muyo. and if you look at their release history that's what happened. everything AIC started with tenchi universe aka space betty and cosmic veronica's wacky space adventure.
because of this OVA 3 would have made no sense and neither would have GXP and so when novelizations became a hot thing in the 90's it seems that eventually he got permission to release them like that from 1999 to late 2000 although some of the things he wanted to have put in clearly got cut so he wrote goodbye 21st century...
That's my take on it anyways.