"I suggest you read more carefully."
Sorry to disagree, but you should be a bit more careful with your writing.
You wrote “some of these groups--the Waldensians, for instance.” Here, the “these groups” refers back to the “apostolic groups [that] existed in the early centuries A.D” you used in the prior sentence. You then follow this by saying “It's really nonsense to claim that all first-century Christians were Catholic,” furthering the connection to the first century groups.
In addition to the history books, I would recommend "Handbook for Writers" by Lynn Quitman Troyka. (Simon & Schuster)
Simply wanting things to be true to fit your personal theology or writing style does not make them true.
Simply wanting things to be true to fit your personal theology or writing style does not make them true.
You mean such as saying the Waldensians were founded by Peter Waldo?
The Waldensians, as most scholars (non-Catholic scholars, that is) agree, originated pre-Peter Waldo (Peter of Lyons), probably in the ninth century. (The term "Waldensian" refers to the Valdenses, or "valley men," not followers of Waldo.) The main proof of this is that their creed, the "Noble Lesson," dates to 1100, before Peter's birth, and mentions the already ongoing persecution of the Valdenses by Catholics.
Of course, for obvious reasons the Catholic Church has no interest in correctly dating the Waldensians.