The ability to count electronic subscriptions on the annual postal Statement of Ownership, Management and Circulation, PS Form 3526, has been established since 2012. I have not revisited the subject since then, when a third page was added to the form to make counting possible.
Newspapers selling e-subs, as commonly abbreviated, wanted to be able to count them on their sworn statement as legitimate proof to advertisers of the additional circulation. NNA worked for three years through various channels to make it happen.