It depends. The system can either pull the current status at the time the booking is made and then store that in the PNR, saving process cycles and DB queries over time. Or it can query the status at various points in the transaction process (e.g. check-in, every time you pick a seat, etc.) which is more expensive but also more likely to be accurate.

And the loyalty and reservations systems often run on two separate platforms. I don't know if that's the case at JetBlue but I know that it is common in the industry.