FWIW I do beleive that what we are seeing depicted in those rings is the story of twins and that the "curious object" is a system to differentiate tween the two. After a priod of time all the objects are on the same hand (same side of the girl, same girl, meaning the other twin is dead). As for the "time frame" of each drawings... this I have no idea. likely months. too many for years, too few for weeks... and there are 9 drawings "in tube" which could represent pregnancy...
great about imola and sforza... was there ever a twin birth amongts the Sforza between 1450-1535 by any chance????