True, there was no need to definitively declare Mary as the Immaculate Conception and her Assumption until the attacks against those beliefs came in the seventeenth and eighteenth centuries.
The Assumption/Dormition was universally accepted by the apostolic Churches. The Eastern and Oriental Orthodox believe in it.
But the Immaculate Conception is quite another issue. For example, Pope St. Pius V abolished the Feast of the Immaculate Conception when he promulgated his 1570 Missal.
It lacked its own Mass proper and was simply referred to at the Feast of the Conception.