I don't have exact numbers. My experience is that the oldest ones, without serial numbers, are smaller. Than they definitely got fatter, and stayed that way throughout the period of blades I like best, especially around 2006-2009, and possibly got a little smaller after around 2012. That is when I started seeing increasingly lighter ones being sold. By 2013 or thereabouts, some of the regular Viscarias were as light as the old Viscaria Light blade, and I suspect they were saving the weight by the way they made the handle (but I don't know that for sure). Why did they do it? Maybe because of increased use of heavier rubbers? Or maybe it was inadvertent some change in the manufacturing process or the wood they were getting? I have no idea.
One of the world's experts on this is a guy who posts under the name of Dean at MyTT. He owns about five of every series of the thing ever made. You can see some of this threads there, as he often posts pictures of his amazing collection. He definitely knows more than I do.
At the end of the day, only Butterfly knows everything about what is going on and they aren't saying.
Incidentally none of these are gigantic changes, but they are things that people (like me) who love these blades and never play with anything else would notice.