does not pay a per-play rate. It pays points, and the rate is only known after the fact.
The instinct is to assume a broadcast pays a fixed amount: so many pence per play. PRS works the other way round.
It takes the money it has collected for a distribution period, pools it, and converts every reported performance into points, weighted by source, because a primetime TV play reaches far more people than a play in a café. It totals everyone's points, divides the pool by the total to get a rate per point, and pays each writer their points × rate.
So a play's value isn't set when it happens; it's set when the pool is divided. Read a PRS statement and you are reading the back half of that calculation, points already earned, the rate they were settled at, and what that produced.