When working for Amazon Creative Services (2010-2014) I was involved in the creation of seasonal styleguides, used globally on retail merchandising graphics. These originated from ideation sessions among designers in UK and US and then led by a the designer whose initial proposal was chosen (or several designers if different ideas were merged).
The examples here below are styleguides I have designed and which were used across Amazon websites, globally. The initial process was a collaborative one, but all ideas, refinements, executions and final assets were carried out individually.
Later in my experience in ACS I was in charge of managing the creation of such styleguides, rather than designing them, making sure they were timely assigned and used correctly.