I’m not saying you CAN’T reduce it to just one time period of history, I’m saying you SHOULDN’T because it’s very limiting in terms of stories you can tell. I know you know this already, but it’s an out of universe change which is why we emphasize pre-1999 (real life) not pre-4000 BBY or pre-1000 BBY or something.
In my opinion, the prequelization of the Jedi and Sith orders should have happened only after the Russan Reformation in 1000 BBY. Darth Bane should have been the first Sith to use the Darth title, and he should have been the one who introduced the “only red lightsabers for the Sith” rule, as well as the Sith aesthetics from the Prequels in general. The same goes for the Jedi. They should have become a centralized and bureaucratized order that forbids romantic relationships and takes infants only after the Russan Reformation. Every Old Republic story that takes place prior to 1000 BBY should have seen a Jedi Order more similar to the one from the Tales of the Jedi comics, and a Sith Order without Darths and red lightsabers.