PADI could infer from their later certifications as to how many divers are doing something at 1 month, 6 months, a year. Beyond that it would be hard, as comparatively very few people sign up for tech courses or instructor courses, which are pretty conclusive signs of someone still diving.
I do not think an inference on later certifications would be valid as to how many divers are active or current in diving because OW certification is adequate to meet most rec diver's needs. There are a lot of divers, me included, that are active divers but are doing everything they want to do without spending the money for AOW or higher certs. It might happen some day, but so far I have seen no need to spend money on a higher cert that would add little or nothing to my diving experience.