Perhaps the data can be compiled better and released much earlier as time goes by? By which I mean a monthly total a few days after the month ends. Perhaps even near real-time! It’s a long while to wait - for example this is the first data for Kenilworth, similar in so many ways to Melksham.
The hourly service is the big difference between the two and the figures there (still to ramp up quite a bit I would have thought) gives you a good idea of the potential at Melksham.
Yes ... Kenilworth is a little smaller than Melksham, but also situated between two other much much bigger places with other rail connections. Its figure of 170,912 looks like a good start and is where I suspect Melksham would be with a
reliable hourly service within a year or two. Double the number of trains and the number of passengers on each of them will be MORE than the numbers on each current train.
Even with the existing service
and it running reliably, Melksham can continue to grow, though slower and to a lower peak. Rejig the town's buses to connect at the station (rather than seem to studiously avoid it) and you'll have a better uplift too.