I know there were some color variances along the years. But I wonder how many of them are due to variances in the paint batches?

I would actually call that lighter Twenty of yours a Bronze. My pictures don't show the color differences on my bikes very well. My RSW is the darkest and has the least amount of sparkle in it. My Superbe is the lightest. My Twentys are two different years 1971 and 1972 based on hub dates and equipment.
Aaron