When did Lego switch from 4 to 6 stud width of Windscreen?
I noticed this, too. But only after the "Speed Champions" came out a few years ago. (I didn't give much attention to CITY.) It seems to me like the LEGO Racers got wider, more detailed sets starting from 2008 or so.

Also: I often check the Bricklink inventory part page (example: 92583), to find the Years Released under the "Item Info" section. I cross reference those dates with the list of sets that an item was used in.