...I would have expected is that there is little known about the car's history prior to the restoration (as in not a single service record pre-dating the restoration)
OK, in the restoration, they rebuilt the brake calipers, changed the pads, replaced the flexible lines, replaced the calipers, replaced the master cylinder, and just for fun, replaced the brake booster too.
Now, of what possible use would a service record from 1983, indicating "brake pad change" and the same for 1989 indicating a fluid change mean? Just fun information. Once you undergo a restoration, what had been done in the past, technically, becomes pretty much irrelevant.
For fun, go and read the information on Metric Motors (Canoga Park, CA) and how they rebuild a Mercedes-Benz motor
and compare that to some local machine shop or your favorite mechanic. The latter may want to know, or ask, "was it burning oil? did you do a compression or leak-down test?" or any number of pointed questions. Metric Motors doesn't care. They take it apart, assess the condition of every part in the engine, and follow a pretty strict protocol on rebuilding. The past history of the motor won't help them. The past history of a car that has undergone a restoration is merely fun history.
In other parts of the collector car world, certain things mean a lot. A "matching numbers" car is very important on some American iron. It's less important on our cars; you just want to see the correct engine. In some parts of the car world, rarity is a direct indicator of value. The rarest of our cars, the 250SL has not seen price appreciation or value because of its rarity.