I will be agonisingly clear.
Your agonizing clarity is failing me. Sorry.
Therefore I cannot know whether my personal details are to be signed by a CA until after the event has taken place.
Huh. This appears to be word salad. There is no CA signing of any part of a payment request itself. None at all.
Why don't you try to explain to me step by step how you think it works and I'll point out where we are occupying alternative universes.
The only signed data is the request to pay, which is signed by the merchant (when used, it's optional), and the merchants own credentials which are part of a certificate he sends (if he is doing the optional signing).
The notional concern that you are talking about is that of generating a proof that a given payment request was instantiated at the users end, such that a webmerchant cannot be accused of sending unsolicited requests to pay.
No. I'm not talking about that at all.
Nothing stops you from sending unsolicited requests to pay.
A payment request is like an invoice, it forms an agreement "I'll send you the things listed on the payment request, if you pay this amount to these scriptpubkeys." the request can be signed so that you known who its from, and the signature is non-reputable so that if they don't make good on the deal you can show someone the payment request (and the transactions in the blockchain) as evidence that an agreement existed and you kept up your side of the deal.