@jreps , sorry for my misunderstanding the AF cohort definition. The current definition of AF cohort is great.
However, we need to remove people who used anticoaguation not only anytime before the index, but also anytime after the index date and before the stroke (That's what the papers you found did).
I don't think removing first time in history AF restriction criteria is necessary.
Could you tell me again the concept_name for '21500803'? I cannot find this concept_id in Athena.