People are allowed to be mistaken about a takana's origin - as were Rabban Gamliel's sons. And I have no idea how widespread (or predictable) their confusion was. But the Chasam Sofer *consciously* misled us on the איסור הלנת המת. As the Maharitz Chiyus observes, according to the Rambam at least, that's בגדר זקן ממרא.
I think what Ploni meant is that throughout Shas we have dinei d'Rabanan derived from pesukim in the Torah. Sometimes the Gemara itself points out the din is d'Rabanan, sometimes we have to wait from Rishonim to prove it and say it's just an asmachta.
People are allowed to be mistaken about a takana's origin - as were Rabban Gamliel's sons. And I have no idea how widespread (or predictable) their confusion was. But the Chasam Sofer *consciously* misled us on the איסור הלנת המת. As the Maharitz Chiyus observes, according to the Rambam at least, that's בגדר זקן ממרא.
I think what Ploni meant is that throughout Shas we have dinei d'Rabanan derived from pesukim in the Torah. Sometimes the Gemara itself points out the din is d'Rabanan, sometimes we have to wait from Rishonim to prove it and say it's just an asmachta.