The encyclical gives a principle, not just an historical account. A principle:
"it was accordingly quite impossible that the Apostolic See should tacitly allow or tolerate such a custom."
Notice the word "tacitly". This means showing approval by silence. It is impossible for the Church to remain silent when there is something practiced repeatedly in the sphere of Her responsibilities that is wrong. I will post another quote later along the very same line that mentions the Ruthenian rite.
Here is the quote I was thinking of...
Omnem Sollicitudinem, 1874:
"the liturgy of the Ruthenians can be no other than that which was either instituted by the holy fathers of the Church or ratified by the canons of synods or introduced by legitimate use, always with the express or tacit approval of the Apostolic See."