No. If Alice reports Bob, the report only includes the most recent messages from Bob to Alice as forwarded from Alice's local copy of their chat. No other messages are made available to WhatsApp. None of Bob's other messages to other people are included, nor could they be since Alice wouldn't have them. In your scenario, if Alice was law enforcement or cooperating with law enforcement, her reporting Bob and then them subpoenaing WhatsApp would only grant them circuitous access to messages from Bob they already had on Alice's device.