If Country A extends MFN status to Country B with reduced tariffs for a product, then it must treat all other nations in the same way. By this WTO encourages multilateral concessions rather than trade-distorting bilateral concessions.
What is the point of granting Country B, the MFN status if it's going to be the same for all countries? Also, the term 'Most Favoured Nation' is completely misleading here. Country A could have announced that it's going to reduce tariffs for that specific product to all WTO members rather than bringing Country B into the whole picture.
Please explain what's the point of a country granting another MFN status, and why does it apply to all WTO members if only two countries are involved here.