Was reverse applique or other cutwork (removing pieces of the applied fabric to reveal the fabric beneath) ever done prior to the 1500s or so? I would think reverse applique would be much easier to do knotwork/Book of Kells designs than conventional applique...
From the paper you referred to, it sounds to me like the applique of
metal work and such was the exception rather than the rule.
Unfortunately she doesn't expound on the applique that was "the most
common method of adornment." I emailed the author though and with any
luck the address is still the correct one, and she will be able to
share some additional information.