Хэлен,

Строгая секретность вытекает из слов Каркарова на суде:
“You must understand,” said Karkaroff hurriedly, “that He-Who-Must-Not-Be-Named operated always in the greatest secrecy… He preferred that we—I mean to say, his supporters—and I regret now, very deeply, that I ever counted myself among them—”
“Get on with it,” sneered Moody.
“we never knew the names of every one of our fellows—He alone knew exactly who we all were—”
И по факту он смог назвать всего 6 человек из всей организации.

Что касается 22-23 октября, это вычисляется по словам Фаджа в Трех метлах в 4 книге. Как шпион сообщил Дамблдору о том, что Лорд собирается к Поттерам, так Дамблдор порекомендовал тем Фиделиус. Прошло чуть больше недели после этого и Поттеры были убиты.
Fudge dropped his voice and proceeded in a sort of low rumble. “Not many people are aware that the Potters knew You-Know-Who was after them. Dumbledore, who was of course working tirelessly against You-Know-Who, had a number of useful spies. One of them tipped him off, and he alerted James and Lily at once. He advised them to go into hiding. Well, of course, You-Know-Who wasn’t an easy person to hide from. Dumbledore told them that their best chance was the Fidelius Charm.” [...]
“He was sure that somebody close to the Potters had been keeping You-Know-Who informed of their movements,” said Professor McGonagall darkly. “Indeed, he had suspected for some time that someone on our side had turned traitor and was passing a lot of information to You-Know-Who.
“But James Potter insisted on using Black?”
“He did,” said Fudge heavily. “And then, barely a week after the Fidelius Charm had been performed—”
“Black betrayed them?” breathed Madam Rosmerta.
“He did indeed.

Это всесторонне обсуждалось на Хогнете.