As far as I am aware, in the old books there was a distinction made between a Solemn Pontifical Mass and a Pontifical Low Mass, just as there was between a Solemn Mass and a Low Mass offered by a priest. The rubrics, of course, were different between them, and there were modifications of the rubrics (and personnel) between Masses said by Bishops and Masses said by priests. Also, as I am aware, whether in EF or OF usage, a Pontifical Mass is simply one at which a bishop presides as the primary celebrant, although you more often hear of a Pontifical Mass being one in which the bishop presides with his pontificalia, i.e. his mitre, crosier, gloves (if he has them), and Pontifical dalmatic. In the OF, there is no distinction between a High Mass and a Low Mass, so the terminology gets a little fuzzy at that point. A Mass celebrated by a priest but presided at by a bishop in choir is not a Pontifical Mass, but a Mass coram pontifice.
-ACEGC