I have learned so much about these classic tracks thanks to Project Cars 2 (and somewhat from other games). I knew about Rouen Les Essarts thanks to NFS Shift 2, but I had no idea about historic Spa. I can't believe I've always known and loved the modern version without even knowing there was a much larger original.
I've only really known about Le Mans since GT5 so I surely didn't know much/anything about historic versions. Only in recent years did I even realize the Mulsanne chicanes were a fairly modern addition. When I would see people driving the no chicanes version I would sometimes think, "c'mon drive the real deal rather than this fake super straight." Little did I know it was once very real, and even so with the Group C cars featured in GT5.
I knew Silverstone classic also thanks to NFS Shift 2, and I had some general knowledge of Monza but only a limited amount. Hockenheim is a bit of an outlier for me. Unlike the other classics, I was actually alive while it was around and I remember (however vaguely) watching F1 races there on TV - I actually remember more playing F1 96/97 on PS1 there and being amazed by the size of it. NFS Shift 2 helped too, with an early historic version that really puts you on edge running through the forrest. I'm still very disappointed with the way Hockenheim was cut down, and specifically how the original layout was completely torn up rather than being kept around at least for historic races.
It's interesting how the version of a track you first learn about can color your perception of the track as a whole. With Spa, I learned the modern version first and came to love it, and am only now discovering the historic version. With Hockenheim, I grew up with the "original" modern, and now I have no sense of identity or purpose with the current disaster.