From the above, it looks probable.
Doing some searches, I found another article which looks disturbing to me:
Msgr. Lefebvre Used to Say the New Mass
How much can such an article be credible? I think that TIA are quite reliable.
From the link above: "You celebrated the “innovated Mass” from the beginning of April 1969 until 24th December 1971.
I would say this is false.
In 1968, we found the True Mass in a basement, by 1969, I was an altar boy for Fr. Bonfil, the first SSPX priest - (here
is a PDF that gives a little history about that era).
46 years ago in 1969 I was only 9 years old, so take this for what it's worth, but I remember that back then, Fr. and some of his group were searching for a trad bishop for his little group of trads and +ABL's name was one that was the topic of many of his conversations and a few of his sermons, I remember one sermon where Fr. said that +ABL did not say the "hootenanny mass".
So imo, if +ABL did say the new mass, I do not believe that he said it for very long, I highly doubt he said it from 1969 to 1971.