But TOCs often keep a record of how many PFs they've issues, with a view to not offering them to those who have had a certain number (I was once told it was 3, but this was in the Wagn days).
Bear in mind those who used to have the money in their hands when caught. If they never had to give their details they'd continue not paying and just paying a PF in full, without argument, every once in a while.
How does a guard/RPI know how many somebody has been issued.
Of course they can ask for details, but if passenger has paid the fare on first request they have no obligation based on the wording of the requirement to provide name and address if they've "Failed to pay fare" as they have not failed by having paid penalty fare at first request.