Fr Chazal said they are using the 1962 Missal because they are "Strictly Observing" the Archbishop's policies.
In battling the crisis in the Church, Archbishop Lefebvre had to say and do many things in the course of his being with the SSPX.
In my mind the most relevant things he said and did would be around the time of the Consecrations and thereafter, when he realised that he was almost alone ( barring other Traditional groups) in the fight for Tradition. All those "hidden supporters" of his in the Vatican would forever remain as such. So hidden, that no one would ever know who they are. Archbishop Lefebvre gave a key interview to Fideliter in 1990, some months before his death.
There is a website which persists in claiming that Archbishop Lefebvre described the then Cardinal Ratzinger as " not Catholic". This same website claims that in his last years the Archbishop felt that his switching from the St Pius X Missal to the 1962 Missal was a mistake, but obviously, Fr Schmidberger the then Superior-General, had the final say in the matter.
The tampering with the 1962 Missal and it's rubrics came much after the death of the Archbishop, and these are ongoing. Would he have gone along with these?.