- So what we've established is just that Netflix has poor video quality on your rMBP, probably due to a combination of the Netflix player not being optimised for the Retina display and the relationship between low-res content and high-res screens described above.
There isn't anything wrong here. It's just the way it is.
Also, a film or tv series being made in the 90s doesn't preclude it from being in HD. Most films and tv shows are shot on film, and quite a lot of them have been rescanned and transferred in HD or 4K resolutions and released on Blu-rays and other media.