I assume they meant a non-promotional newsletter that isn’t from the manufacturer.
Those do exist, but not all doctors read them. However, those same doctors might spare 10 min to have a manufacturer rep stop by to answer questions.
I’ll also add that doctors aren’t dumb. They know anything from manufacturers is biased - they want to sell drugs. They usually rely on other physicians to give them info on real world experience with a drug.
Even if they did, that would literally be marketing, which is what you're apparently against.