Thought On The Study Of The Laws

The Gemorah in Pesachim 6 brings the source for the law to learn and ask (or ask, depending on the text) about the laws of a holiday 30 days beforehand from Moshe teaching the people about Pesach Sheni 30 days beforehand, on Pesach.  The Beis Yosef in siman 429 cites the view of some Rishonim that hold this law only applies to Pesach because of its many laws, not to other holidays.  This would seem to be the view of the Shlchan Aruch that cites this law regarding Pesach (see however Bach.)  How can this view be correct if the very source for the law is said regarding Pesach Sheni that doesn’t have all the many laws that Pesach does?