It appears that Drew used FFE when preparing to write his book, so – applying Occam's razor – I reckon this elusive line from Reorte to Riedquat and beyond is a line on the FFE map. So what you're looking for (perhaps) is a system in FFE, south-west(ish) of the Lave area, which also exists in Elite Dangerous. I had a quick look at the FFE map here, but nothing leapt out at me. It could be further out, of course, or I may have missed something. "Whether it's found depends on who goes looking" could mean "Whether it's found depends on whether an FFE player goes looking".
Umm... if that's true, if plotting the R-R line in both ED and FFE, do you end up in (roughly) the same part of the galaxy?