The question then becomes what were the traditions at the time of Paul?
That’s an easy one. . .all the ones that Catholics call Sacred Tradition. (Really. There is NO more revelation after the Bible, and I’m not even going into the 382 A.D. date for the written one).
All the things of Sacred Tradition, including the discipline of priestly celibacy in the Latin rite, the Immaculate Conception, the co-equality of the Trinity. . .these are not part of the “written” tradition of our beloved Sacred Scripture, but ARE a part, traced through apostolic works through the early Church Fathers and all the way to today (and to the future). They may not have been fully known, fully realized, or fully explicit, but they were there.
Paul lived in a time when slavery was legal and practiced. . .with some minor and some MAJOR differences from the slavery of say 19th century Europe and America. Do we think that the Bible “changed” its position on slavery, or do we think that as people grew in the word of God and followed in the way of Christ that people better understood slavery and thus worked to end it?