Haleivi:
The distinction is not made up. The pasuk says ?? ????? ???? which seemingly refers to the lischas hagazis. The Rambam holds that it applies only to the Beis Din Hagadol. See the ??????? ??? on sefer hamitzvos ‘??? ????? ??? ?. And see the Mishnas Yaavetz Choshen Mishpat siman 6 where he explains that the machlokes between the Rambam and the Sefer Hachinuch (about whether the obligation to listen applies even to a non-beis din hagadol) is Taluy on the Machlokes between the Rambam and the Ramban regarding whether kiddush hachodesh requires a beis din hagadol. He explains based on the Sifri which comes to include the Bais Din Hagadol in Yavneh, that the Rambam holds that it’s coming to give Yavneh the status of the Beis Din Hagadol whereas the Ramban holds that the status of Beis din Hagadol is determined by ????? ???? and therefore the Sifri is coming to tell us that even though Yavneh does not have the status of the Beis Din Hagadol, you still have to listen to them because the obligation is to listen to the Chachamim in every generation (like the Sefer Hachinuch says).
benignuman: While it is a machlokes (as I have just shown), the Sefer Hachinuch does in fact invoke Yiftach b’doro k’shmuel b’doro.