“The initial spark of the idea for this research arose when someone asked me if I believed in horoscopes. It got me wondering if there could potentially be a biological basis for them, in terms of how a person’s birthday could be associated with physiological or mental features.”

Hmm… the seasonal differences in diet and environment are probably greatly reduced in modern times, compared to when astrology developed. So maybe trends like this used to be even more pronounced.

I suspect it’s a difference between the sell-by date (AKA shelf life) and the expiration date—most contraceptives would be expected to be good for at least a few years after purchase.

What about the usage demographics within each country?

In underdeveloped/exploited countries, internet usage is more likely to be concentrated among the economic elites who formerly benefited from colonialism—so if increasing adoption in those countries just follows the pattern of other internet use, it could have the opposite effect from the one intended.