"Pest Control Office" (PCO) is Banksy´s official organ. They do not "authenticate" any street work.
All street works are described as "attributed" to. It means to consider as made by the one indicated
especially with the strong evidence but in the absence of 100 % conclusive proof.
If you do not understand this please do not send enquiries and do not expect an answer.
PCO will never issue formal COA´s for what is considered street. No need to ask.