Comment by bigiain

Given that the only information we've got to go on is the open letter - I'll point out this bit and take it at face value: "They forwarded me an email you sent them asking for an explanation but of course they lied to you and said they didn’t know who was responsible."

I think it's 100% plausible that the agency accepted Lee's decision on which poster design to use as "last word", while not fully disclosing (and perhaps even actively deceiving him about) the payment/negotiations/contracts/copyrights with the designer.