The nearest date that I have come across for the start of fitting the PRT to the TF is the rather vague "mid 2003" referred to in Des Hamill's book 'The Rover K-Series Engine'.
However, it must be taken into account that this will refer to the build date, not the sale date so it is likely that the majority of TFs sold and registered in the three or four months after the start of it being standard fit on the production line would be non-PRT cars. It is also a sad fact that a great many TFs sat in both storage at Longbridge and in dealers yards for many months before being sold and registered, and it is likely that there will be a number of TFs registered in 2004 that will have been built prior to the PRT becoming factory fit.
As Chris T has already mentioned, there is no real evidence that the PRT had any measurable effect on the incidence of head gasket failures in any of the vehicles it was fitted to.
Edit: a bit of further digging in a parts epc suggests that the PRT was fitted from VIN/serial number 622951, although I am not sure what the off-assembly date would be for that VIN?
I missed these updates. Thanks all. My vin is 628xxx so maybe it has been taken out I haven't yet checked whether I have a blank thermostat.
Ibm want to renew some of the engine bay hoses so I have to make a decision as to what to do. My reading suggests a PRT at tge dront of the car might be the better solution but I also read someone saying it made their cabin warmer. I don't need extra heat in the cabin, does anyone have experience of a PRT at the front and added cabin heat?