This question is tossed in as a search for info, not to stir up trouble ..

For years, I've read the figs people talk about frequent races as though it's a bad thing - as though four races in six weeks is an unusual, taxing thing. It hasn't been all that long since it was perfectly ordinary for Preakness and Belmont horses to have four races within a month and a half or so, perhaps even exceptional if they didn't.

Have these methods of analyzing races evolved since then? How exactly do they address the topic of horses improving or maintaining form and the frequency of starts?