Think of the philabeg worn by Rob in the film Rob Roy: unpressed box pleats, narrow front aprons, no fringe, etc. Highland dress historian Peter MacDonald was the costume consultant for that movie, and that's what he believes early "little kilts" were like.
The notion that the first philabegs were hand-pleated each time by the wearer is a "reenactorism" unsubstantiated by any period documentation or image. Did they have a drawstring or belt-loops? Were the pleats stitched into place from the get-go? We simply don't know, as none survive from the period of earliest use. The earliest surviving philabegs date to the 1790's and feature sewn-in box pleats. Does this represent earlier practice? Probably, but again,we don't know for sure....