I decided to try to figure out more closely the actual numbers in India, as 2 million is clearly an exaggeration, when the Indian census says less than 5000. So I've been using google maps, selecting an Indian city with over a million people, and then using the 'search nearby' for Baha'i centers. So far I've only found around 10 centers. So that's one for every 200 000 people. I have no doubt it's more than 5000, but no way is it 2 million.
It's a difficult task for a ton or reasons ... illiterate villagers will sign anything, and it may be membership cards
... there is no dropping off the list for inactivity, unless the person requests it, and all those inactives are still counted. Notice that the wording is always just membership, and not 'active membership'.
That second one is common in other faiths as well. A friend of mine was surprised to learn he was on the roles of a small town church here despite not living in the town for over 20 years, and being inactive. Dad was probably listed as a member of the United Church of Canada his entire life, despite his renouncing it when he was 10 years old. Bottom line is nobody would care. I wouldn't care about exaggeration of numbers of nobody used it as a message of growth, or promotion.