Awesome find! I'm looking it over. I could really pick a specific decade depending on whether I add elbow cops, etc. It's a shame it doesn't go back into the 13th C at least a little bit, but it's the 14th where things start changing rapidly, so I can understand that.
I'd love to get some reliable info on when my style of great helm went out of style. We know of course that it evolved into other types of jousting helms, and the pembridge style great helm worn with a bascinet existed later than the simple great helm I use.
In his charts, the great helm looks like a minor fad later in the 14th, but of course we know they were very common in the 13th leading into the 14th. I just think they weren't common in effigies because they wanted to show the face, so you tend to see the coif alone (EDIT: Hah, I just noticed he says exactly that). He also comments that the mail coif in most cases would have a great helm, making it look like they saw pretty solid use through the entire 14th, but like I said, that contains the later styles than the one I use.
Very fascinating page!
EDIT: It also confirms that I'm totally fudging the date with my spaulders... they don't really start appearing until the 1340's, but most of the rest of what I'm doing is still believably in the 1300-1310's.
