[sinkspur]

I'm looking for documentation.

Here's something from the infamous Father Scott of the SSPX, written upon the defection of a Father Vanderputten from the Society:

He himself has obtained a celebret from Cardinal Ratzinger, and now celebrates the Indult Mass, under the condition that he places himself under a diocesan bishop within six months.

Source.

Again, I would find it odd that the Vatican would approve of a "free lance" priest celebrating the Tridentine Mass outside the jurisdiction of a bishop. Every priest has to be attached to a bishop or superior.

[ELS]

I'm looking for documentation.

A few hits in Google for: celebret Tridentine "Ecclesia Dei"

6.Since a number of older and retired priests who have a deep appreciation of the previous Latin liturgical tradition have approached their individual ordinaries as well as this pontifical commission to obtain the celebret for the use of the 1962 missal

It will be noted that any priest requesting a celebret can be granted one without the agreement of his bishop. It is necessary only to inform the diocesan bishop that it has been done. It will also be noted that the 1962 Missal is mentioned specifically, as was the case in the motu proprio Ecclesia Dei.

They [sacristans at St. Peter's] are also requesting from all priests who wish to offer Mass according to the 1962 Missal to produce a celebret which is issued by the Ecclesia Dei Commission. While the Commission has the authority to issue celebrets without authorisation by a diocesan bishop, it has issued few if any since 1989.