I am not being critical of those who think they have the 'correct colour' for a model, but matching old colours with new is more or less subjective. The first thing to decide is exactly what you are trying to achieve - a match to the original colour, as originally applied to the full size object, or a colour which looks right on a model, even though the effect of size, ambient lighting, surface finish, etc. is entirely different. You can go back to the original paint composition, if you can, and then remix using the same composition. You may or may not get the same result, bearing in mind that the original mixes would have varied between locations/periods, but without a time machine, you can't tell. At the end of the day, the best you can do is make a guess, based on whatever research results you have obtained, see if it looks right, and decide if that has to be near enough.
Even if you have an original sample, kept out of daylight for all its life, what other chemical degradation has occurred? Is it linear? Then layer on top of that photography, lighting, vdu/print colour space, many folks' unknown colour blindness, the impossibility of scaling nature, and you can imagine the fun that ensues. It all becomes a bit of a religious argument, completely pointless, a bit like the slightly older one about 'how many angels can sit on a pin head'.
I have no specific interest in the LB&SCR, but I am interested in how folk think they can replicate colours from years ago, and be certain they are 'right'.
Best wishes,
Ray