It is, therefore, permissible to celebrate the Sacrifice of the Mass following the typical edition of the Roman Missal promulgated by Bl. John XXIII in 1962 and never abrogated, as an extraordinary form of the Liturgy of the Church.
-Motu Proprio Summorum Pontificum
As for the use of the 1962 Missal as a Forma extraordinaria of the liturgy of the Mass, I would like to draw attention to the fact that this Missal was never juridically abrogated and, consequently, in principle, was always permitted.
-Papal Explanatory Letter
