It's not possible to have a selvedge on four sides of a piece of cloth. The self-edge is a function of the weaving process and only occurs at the sides. The ends of a traditional plaid were turned and sewn (hemmed) - see my articles on Selvedge techniques and Joined Plaids

In the case of the 'full border' the cloth in both plaids had a selvedge pattern that differed from the main sett and this arrangement was woven at the beginning and end of the cloth in the case of the single width piece and for the double width plaid was woven twice in the middle too.

The technical skill to weave the double width plaid was considerable because it wasn't a case of simply weaving a length, cutting it in half and joining the two lengths, each run before and after the central border section had to have the exact same number of repeats for the pattern to align once cut and joined. If that was not clear from the paper then perhaps I need to amend it?