Hi Mark,
There was also probably a lot of variation in materials and colors occuring when Triumph sourced from various vendors themselves and, those vendors in turn sourced raw materials from different suppliers. It's not all that unlike the situation today, I'm sure!
Case in point, my TR4 didn't have the "fuzzies" or "draught excluders" that supposedly all were fitted with. It's got hard plastic trim instead. I suspect this was done because of the fairly unusual Midnight Blue interior that was original to the car (quite a bit darker than the more common Shadow Blue) and perhaps "fuzzies" were only available in the lighter shade (which looks weird combined with the darker vinyl & leather, IMHO).
Another example is TR4 carpeting... I've seen at least a half dozen clearly quite different, but all supposedly "correct" medium grey shades. Worse, none of them are anywhere close to matching the small samples of original carpet I eventually found in the car (which might have discolored, too, so is pretty useless as a guide).
And, the hard top I just got has its original headliner. The material is a perfect match, texture-wise, for the sun visors that came with the car originally. Unfortunately, the visors were dyed black (this was often done by the dealer, originally visors were white) and the headliner has turned cream colored and brittle with age. So, I've ordered a new headliner and will be trying to match it with visors.
A more modern example, the interior of my '97 Land Rover, which I would expect to match, has definitely faded to different shades over the years. Some harder, plasticky materials like the gearbox cover and the center console faded a lot faster and have ended up a noticibly lighter/different shade than the leather seats, center console lid, door panels and dash/air bag cover.
So long as the kit you got all matches each other and is reasonably close, I think anyone would have a hard time arguing about its "correctness".
Again, just my opinion, but I think Stone will look absolutely superb in a your red car! Keep us posted!