One of the reasons why these photos look so convincingly realistic is the same reason https://en.wikipedia.org/wiki/Chroma_subsampling is done --- the human eye has less sensitivity to colour resolution, and so even relatively vague blobs of colour can evoke the right perception as long as there is sufficient luma detail (provided by the original monochrome image); but if you inspect the photos closely, you'll see there are plenty of unnatural gradients in clothes and such, and the colours of objects blend into each other.
This was my thought too - it may not matter if the colors are 100% accurate as long they are enough to trick the human eye and brain into filling in what’s missing. Besides, the reality is, these are not color source photos and will never be. A black and white photo does not contain the color information, it was never captured. All we really can do is use historically accurate colors and afaik, that is the same thing professionally recolorists do as well.
