Part of our unique timeline is a 400 year darkness that ended in 835 ABY. This is when our board began and PC's began taking back the reins of history. There have been a multitude of player-created Jedi Orders, Enclaves, Praxeums, Academys, Networks, and Sects ever since.
To my understanding there was never any continually operating Jedi Order that survived the 400 year darkness. However, that said. Many PCs on this board are thousands of years old according to their backstory and have served in ancient Jedi Orders. So you can still find holocrons and even first-hand accounts of what Jedi were like even before the Gulag Plague.