Anyway, here is a potential problem with Nagarjuna's reliance on Ratnakuta Sutra: If we just blindly "accept what the world accepts" then, on the conventional at least, "a Madhyamika's principal epistemic task [is] just to passively acquiesce and duplicate." (MS152.)
It is a trivialization of the idea of truth. If truth means nothing, then qualifying it with "conventional" or "ultimate" adds little.
First things first -- truths (satyas) are objects of cognitions -- which can be either correct (ultimate) or false (relative). Since you are studying Gelug influenced discourse, this may not be immediately evident to you.
This means that if you see something that you identify as salt, and it functions as salt, this cognition is true in so far as it is efficient.
When you analyze that appearance for some fundamental saltiness in that appearance of salt, that cognition of salt fails because no fundamental saltiness will or can be found. In other words, relative truths are true so long as they are not investigated, that is, so long as the appearance which produces the cognition which lables that appearance is not analyzed to discover whether or not there is an essence which produces the identification of the given appearance in question.
A relative truth is the subject of a cognition that is not in possession of the fact that the given apparent phenomena being perceived as an object of said cognition lacks the identity imputed to it. An ultimate truth is an object of a cogniton which is in possession of the fact that the given apparent phenomena being perceived as an object of said cognition lacks the identity imputed to it and does not perceive the identity which is non-existent in that object of cognition.
The function of the two truths is to lead to the cessation of proliferation about identity. The lack of identity within phenomena and persons alone is emptiness and nothing else.