I have an old Modern Drummer from the 80s where Phil Collins is endorsing both Pearl and Gretsch (or maybe Pearl and Tama) in the same issue. I think it was just a scheduling error in the advertising department.
I have that issue too...It's Pearl and Gretsch. I think Phil's departure from Pearl was very sudden and when he called Gretsch they were quick to snap him up and ready to publicize it. For their part Pearl is still using Phil in ads today, in spite of the fact he was only on their roster for about a year.