My take is that both upper and lower sail ranges of a board changes with rider weight. Of course, other things, like sail type, skill and preference might have just a big an effect, but for a "given" rider (conceptually speaking, one given rider can not, at least not at the same time, have more than one weight) sail range vary with rider weight.
But in my experience, it is not as easy as a simple shift. This follows from another fact, namely that for a given board type and saior, there is often one board size that give the maximum sail range. A bigger board will loose more on the high wind side than it will gain on the light wind side. And vice versa with a smaller board.
But the question is of we should create som kind of schemata showing this? I'm not sure its such a good idea since there are also all the other variables (skill, preference etc) that is kind of hard to quantify. Maybe a sensible way to do it is to just hint that the rec sail sizes are just indications for a "general" rider.