Of the currently operating ones? I doubt that. Even just within that list there's a significant percentage of link rot present. Beyond the top ~5000 or so sites I would wager the longevity of adult content sites is pretty bad on average. They tend to be sketchy, ad-infested cesspools after all, that lose their value for the operators once they get on block lists.

I don't doubt that there's a lot more out there (10x yes, 100x possibly, 1000x unlikely imo), but I think tens-of-thousands is enough to capture almost all of the significant ones that get any traffic and will be around for longer than one or two domain renewal periods.