see i think you have the basic understanding of some things wrong
first of all
who says they can't harvest twice? after september 21st, anything that's started will go into flowering a lot faster than it would if planted in june or any time after the spring solstice. secondly, to harvest twice, all they'd have to do is plant one half of the seeds when the other half is halfway done. for example, plant the first batch in april/may, and plant the second batch after monsoons. the first one will probably take a little under a full year to finish, while the second set of plants will take probably less than half that time due to photoperiod. the harvests will probably be a matter of anywhere from a month to 4 months apart depending on when they plant. assume that in general, as far as indian sativas are concerned, the plant requires x inches of height and a minimum of 12 hours of darkness to flower. with normal plants, regardless of whether or not they've reached x inches (or x amount of budsites, mass, or whatever the plant uses to quantitatively decide) they will start flowering if under 12/12. however, these sativas in the south indian half of our continent have the minimum size to reach before flowering as a more important pre-requisite than photoperiod. flowering will only happen if the size criteria has been reached and the photoperiod is compliant, within reason. while equatorial sativas don't care as much about the photoperiod, that is still the primary influential factor in inducing flowering. that is why your preflowering was short. also, i wouldn't take any of the things i said as HARD and FAST rules...there are bound to be exceptions and this is only my first grow. if you ask me, your plant is still in the preflowering stage...my plant also went through a similar stage where pistil production stalled, pistils became brown, and only recently she started developing more pistils and calyxes.
and from my understanding, if you're growing a plant under 12/12, preflowering indicates a start in flowering for normal hybrid strains - it is a sign that heavy budding will follow shortly; that is not the case with our equatorial sativas. the preflowering (i think) happens so long before the actual flowering in the wild because the males will be done well before the females are done budding. however, the pollen will need to be collected when released by the male plants ; the pistils, if you observe, will be coated with small baby trichomes, which will be able to trap floating grains of pollen, something that cannot be done without pistils. this will maximize the plant's chance of reproduction and make it more likely to produce seeds for the next season.