Yonatan Schreiber, a Brit, though he seems unlikely to mug me at a soccer match, asked me if I accept the Rambam's Eighth Principle, which says: "One must believe that all parts of this Torah that we have today is the Torah that was given to Moshe who got it in turn from God himself. If any person is of the opinion that any anecdote or date is superfluous he disbelieves that Torah is Min Hashomayim."
The answer, of course is yes, I do accept the Rambam's Principle, but let's recall that we're dealing here with a two-tiered verity, ie: the truth of fact, or reality, and the truth of law.
Often reality is set aside in favor of law. If a piece of pork, for example, were to fall into a very large vat of kosher meat, it becomes kosher according to the laws of bitul. The law says that under these conditions, the pork is kosher; though the facts haven't changed: it's still pig meat.
Two famous Talmudic stories validate this principle. In the case mentioned in Rosh Hashana 2:8-9, Rabbi Yehoshua celebrated Yom Kippur according to the calendar reckoning of his rival, Raban Gamliel. Though Rabbi Yehoshua continued to insist on the reality of his own position, and his own calculation of the date for Yom Kippur, in practice he conceded to the law, as set forth by the Nasi.
More explicit is the dispute between Rabbi Elazer and Rabbi Yehoshua. (B. Metz 59b) In that story, Rabbi Elazer defied the law, as set forth by the majority, and was excommunicated - even though God Almighty Himself served as his defender. God represents reality. He can't ever be wrong. Yet, in this story even He bowed to the law.
When the Rambam articulated the Eighth Principle he was speaking as a jurist, not a historian. His ruling, therefore, has the force of law, not fact.
As an historian, the Rambam has, perhaps, been overruled by historians with access to tools that weren't at the Ramabm's disposal, tools like archeology and linguistics. The same Rambam who told us "Do not ask me to reconcile everything that they (the sages) stated about astronomy with the actual reality, for the science of those days was deficient, and they did not speak out of traditions from the prophets regarding these matters (Moreh Nevuchim (3:14) )" would likely concede, when faced with the scholarship of the last 200 years, that his own knowledge of antiquity and of ancient languages and practices was deficient. He might even admit that the truth of the Eight Principle as a matter of fact was open to question.
What can not be questioned, however, is the law. As a jurist the Rambam can not be over ruled. The law says Jews must believe that the "Torah that we have today is the Torah that was given to Moshe who got it in turn from God himself," and so I believe. I accept the law, though, like Rabbi Elazer and Rabbi Yehoshua, I can't avert my eyes from the possibility that, in this instance, too, law and fact do not coincide.