And what are the specific rules on an undated Rover box? Are they in the public domain?
I think you're misunderstanding my comment - I agree that there does not appear to be any written explanation of how an undated Rover ticket should be dealt with. I was trying to make the point that there is a contrast between how this situation would have to be dealt with and how (for example) an Advance ticket discrepancy is dealt with.
The lack of clarity around it could lead one guard to 'show discretion' and hand over a pen, whilst another may decide to go into a verbal warning about dating boxes before travel. I doubt any would get stroppy enough to suggest that the undated ticket was technically invalid and a new single would have to be purchased, but you never know
There is certainly nothing that I can find in NRE's webpages about undated boxes on Rover tickets, I'll have a look in work when I'm next there to see if I can find anything 'on the system', so to speak.
Take the other extreme from the example I gave previously - it's the final day of a 3 in 7 Rover's validity period, none of the boxes have been dated - the person could have been travelling all day every day for the last seven days and been lucky not to be inspected. OR, they could, through personal circumstances, not been able to use the ticket they had already bought until today and decided to at least get some use out of their wasted money. Either way, they forget to date it before meeting the guard. Now what do you do?