It's very difficult, in part because De Rosa was less consistent than other marques in this regard. This was in part because De Rosa was still a low-volume producer in the 70's, making a relatively high percentage of team and custom bikes. So you see chronological overlap between features like heart BB cutouts vs. slots, long-point vs. short-point lugs, more vs. fewer heart cutouts, etc. Having said that, I know Hilary Stone has been compiling info on De Rosas since he started coming across and acquiring them a couple of years or so ago. I think we can expect a timeline from him, hopefully sometimes soon, that will at least give us a jumping off point. I'm happy to comment on features I know something about, which is a few but certainly not all of them, as with Colnagos I'm more interested in some vintages of De Rosas than others. I lose a lot of interest around 1980 when De Rosa went to cast lugs.