Those diamond-shaped buttons have been in use at least since the early 1950's when my Montrose doublet was made and probably long before that. As to other buttons, the aristocracy used to have whole suites of accessories made, all matching, with sporan, dirk, sgian dubh, buckles and a set of individually designed buttons. While not aspiring to those ranks, I had a set of silver buttons made for my sheriffmuir, square with a celtic knotwork design and for my Montrose/Kenmore round silver ones, again with a celtic knotwork design.