I agree with Steve about reading too much into this and in effect trying to codify a process.

Looking through my pre-1860 photos of old military and civilian kilts I can't find one with a strap and buckle. Generally they are closed with ribbon/tape ties or buttons. That doesn't mean that one might not find an example of a buckle being used by around the middle of the C19th but I suspect that they are later and that even when they did come in that there would have been a number of styles.

Just a thought but I wonder if their use coincides with the move to knife pleats and more cloth.