I agree it is a bit of a grey area.
But we need to consult the
NRCoC.
Do they cover the entire journey? Yes; the tickets are valid Manchester - Glazebrook and Glazebrook - Llandudno
Is one of the tickets a Season ticket? Yes.
Is the ticket issued on behalf of a passenger transport executive or local authority? No
The other ticket(s) is/are not Season tickets? Yes
So what part of Condition 19(c) does it fall foul of? (without inventing a non-existent rule)
It isn't a season ticket from Mauldeth Road to Glazebrook though. It is a season ticket from Mauldeth Road to Salford. The definition of a "Season Ticket" according to the National Conditions of Carriage is:
"...a ticket which allows you to travel for a
period of 7
consecutive days or longer and will have (except in the case of an Electronic
ticket) one or more of the following characteristics:
(i) it shows the word Season;
(ii) it shows the word Travelcard;
(iii) it is endorsed with a photocard number"
Which for a journey from Mauldeth Road to Salford, it passes. With this, I have no quibbles. For a journey from Mauldeth Road to Glazebrook, it allows travel for just two days. So I don't believe by the letter of the law it should count as a season from Mauldeth Road to Glazebrook. It also cannot count as a leisure travel pass as it is too short in duration. My interpretation of the rules is that the season ticket element of the product, for the purpose of the intended journey in the OP, would end at Deansgate.
Even if we treat it as a season, I'm not sure I agree with your assertion that it isn't issued on behalf of a PTE. The extra validity is something decreed by TfGM, the local PTE, rather than the train operators, is it not?
Regardless of the above, and the rights and wrongs of it all, I think it is good that the company have erred on the side of allowing it, however, as it's one of those situations which is going to crop up very rarely in the grand scheme of things, and the rules weren't written with situations like this in mind.