Didn’t realise you could use two rover tickets (as opposed to one rover ticket + standard ticket) on trains that don’t stop at the border station.
So presumably you can travel from Warrington Central to Burton on Trent using A TfGM Wayfarer and a Derbyshire Wayfarer on the EMR Express trains from Warrington to Sheffield and Cross-Country from Sheffield to Burton on Trent?
Yes, non-stop combination of two rover etc. tickets used not to be permitted - but that changed with the introduction of the NRCoT in 2016. Equally, the NRCoT abolished the ability to string along multiple singles/returns with a rover etc.
Technically it could be said that non-stop splits aren't permitted when combining TfGM and Derbyshire Wayfarers, since the two have overlapping validity between Grindleford and Chinley (for trains that run via Stockport) and the NRCoT require that:
the last station at which one Ticket is valid and the first station that the other Ticket is valid are the same
...but in my eyes this would be an excessively literal reading of the condition. I cannot imagine a sensible reading resulting in the conclusion that tickets with overlapping validity eliminate the right to non-stop splits!
Bearing in mind this is a consumer contract I would have said this reading must prevail. In practice, I think it unlikely that any member of staff would be so familiar with the NRCoT as to even try and pull anyone up on it. It's more likely they would wrongly claim that non-stop splits aren't permitted in general, or (more likely, you'd hope) simply accept it as valid!