There are plenty of articles from May 2020 that all discuss in various words that a deal was struck. If you believe that AZ didn't sign a contract with the UK before Aug 28 then the burden is on you to prove that.
No, there are plenty of articles from which you deduced there was a contract signed by the UK before august.
It's impossible to prove there wasn't a contract signed, it is however possible to prove a contract was signed. Your articles never provided evidence for the date the contract was signed.
It's impossible to prove there wasn't a contract signed, it is however possible to prove a contract was signed. Your articles never provided evidence for the date the contract was signed.