The immaculate conception was always a teahing of the Church, just as the Divinity of Jesus was. It was just not defined until the 19the century.
The Divinity of Jesus - which had always been a teaching of Christianity - was not defined de fide until 325, just as Immaculate Conception - which had always been a teaching of the Church - was not defined until 1854.
When the Church defines a dogma it does make it up at the time. In simply defines the particular doctrine and makes it a domga of the faith.
Therefore, when the Blessed Mother told Catherine Labore that she was the Immaculate Conception, it was not contrary to what the Church already taught - even though the particular teaching had not been defined de fide.
In the same way, if there was a private revelation in the year 250 that said Jesus was Divine, it would not have contradicted what the Church taught - since tht has always been a teaching of the Church.
Now, I didn’t demand that JR accept the teaching found in the book. I simply said that it would be best to adhere to that teaching rather than his own opinion that is contrary to what the teaching of the approved revelation and no where to be found in an approved Church document - at least not that he knows of. In other words, it is better to hold to what is taught in an approved source, rather than our own opinions.
I hope that helps.