First Principles Thinking: updating the IPS after material changes
B is correct. The CFA Curriculum requires an IPS review prior to material changes to investment decisions and recognizes that changing circumstances (wealth, liquidity, risk tolerance) drive updates. Once the IPS is properly revised, suitability is evaluated against the updated written objectives, mandates, and constraints.
A misapplies the diversification guidance: the curriculum itself notes that some reasonable amount of diversification is the norm but explicitly allows higher-risk or concentrated positions when consistent with the client's objectives.
C invents an independent-analysis gatekeeper not imposed by the standard; Quon's duty is a reasonable inquiry and consistency with the updated IPS, not external validation.