OP, sorry but you are making this difficult.
We'll explain procedure then you can fill in the gaps.
1. A vehicle may only be removed if a PCN has been served;
2. The OBCEO would INSPECT the PCN to ensure that it's correct before looking at other circumstances and council policy and authorising removal. In 99....% of cases a PCN is still on the vehicle when the OBCEO attends;
3. But not in your case, you'd removed it!
4. I still think that what you saw could have been an empty envelope but NOT because another PCN had been served but because perhaps this is a signal to the pound that a PCN had been served and that proper checks had been made. IMO, leave this line of thought, I don't think it's going anywhere and is a distraction;
5. This deals with what happened at the roadside, now for the pound which is a separate process under different regulations;
6. Post the receipt you were given when you paid to recover your vehicle and all other notices related to payment and how to make representations which by law had to be given to you at the pound. Only delete your personal info.
I posted all 3 documents I received further up. It was 1 PCN issued before the towing, document with how to recover the car, document on how to appeal.
You are right, it was an empty envelope. I only mentioned it because it seemed strange as I had already recovered the ticket. The main point is that my car was towed from a disabled bay which seems to be questionably enforced and lacks signage + attempt of removal of the lines.
I have added a screenshot of the payment request from the car pound via email and also the receipt of payment below.

