So the question is why did early and not so early CD players have rather variable J-test results? It is possible I still have the results on an old hard drive, but I measured some very early players and a couple DVD and a couple bluray players at one time. I still have the ADC used to measure and with current equipment know it had low jitter of its own as an ADC with a free running clock. I still have the goofy Pioneer DVD player (assuming it still works, did two years ago). Goofy because if you change tracks jitter goes sky high dropping to rather low levels over something like 12 seconds.
I don't know that this patent is exactly relevant, but clearly the issue of rapid track selection has been an issue:
...in case the rough actuator is driven at a high speed for a fast access, the focus lens held by the fine actuator is deflected due to the acceleration caused at the start or halt of the rough actuator or by the vibration induced during the travel thereof, so that the fine actuator is kept in vibration for a while even after the halt of the pickup-base in the vicinity of the target, thereby raising a problem that the fine actuator cannot be brought into servo control with stability and rapidity.
https://patents.google.com/patent/US5117410
Maybe my claim that the system was immune to transport quality might not be
absolutely true for systems that allow increased errors following a track change in order to speed up track access...?
It could also be as simple as power supply instability affecting the clock oscillator..?
It's difficult to find actual evidence that the basic system has always been the same and (conceptually) perfect hence the grubbing around in data sheets and patents. But the book "Understanding and Servicing CD Players" by Ken Clements includes the following extracts:
Putting those together, I think, makes the case that audio players have always worked the same basic way.
I am keen to quash the idea that CD players are, or have been, like a glorified record deck: an electronically regulated motor speed (using a crystal don't you know) with subsequent electronics that adapt to any instability in that speed. This is, and would always have been, the wrong way round. The motor is ultimately regulated by a crystal, but not for perfect short term stability; merely adequate stability to maintain the correct average rate as demanded by the central crystal oscillator.
P.S. Apologies for that green colour - a random selection and, I now realise, rather unpleasant