Yeah, by the mid 14th, the great helms had pretty much evolved into more of the round-topped Pembridge style, and were usually worn over a proto-bascinent sort of cap that was integrated into the coif. This is hard to do with off-the-shelf gear. The helms can be found online, but not so much in the way of these proto-bascinents that will fit inside. So most people just end up wearing a regular coif, I think.
