For the benefit of the other readers, I presume you are referring to Q&A 512. A drug’s MOA is an objective and intrinsic pharmacological property of the drug. It requires more than a couple of in vitro studies and/or review papers to support it. Generally, such claims are required to be supported by the TMA as discussed in the following PAAB tip document: https://secure1.paab.ca/Marketing_Benefit_Claims_-_June_22.pdf
Sources like authoritative consensus guidelines or medical textbooks can be used to support pharmacologic classification. Additionally, they may be considered to elaborate on the existing mechanisms in the TMA where there is ample alignment among various medical texts and guidelines, but a detailed presentation of the MOA from those sources would conflict with a product monograph which states that the “the exact mechanism of action is unknown”. Thus in cases like Q&A 512, the TMA would generally require updating prior to consideration of a more elaborate MOA presentation.