Your PIM, your commerce engine and your OMS each hold part of the truth. A person shopping on your site gets a composed record. An agent shopping across twenty retailers gets whatever you expose on MCP, and most catalogues expose nothing because the fan-out would be unmanageable.
Building a second model means maintaining it forever. Reading sources live means reliability compounds downward: one source at 97 percent uptime, ten sources at 74 percent. You cannot let an agent write into your systems, so checkout needs a quote with stated validity. Token cost per query matters when Perplexity is calling you a thousand times a day.