I have a weekly ticket from Gravesend to "London Terminals", plus high speed. Despite myself actually choosing "city thameslink" as the destination when using the ticket machines, or saying it to the ticket counter, the ticket always comes out as "London Terminals". I go from Gravesend to St Pancras via High speed, then take the first capital connect from st pancras to City Thameslink. I have been using this route for 5 months now, and on the odd occasion that my ticket has become mangled and not working through the barriers any more, staff at both city thameslink and st pancras have not challenged the validity of my ticket and let me through. All of a sudden today, I was harassed by staff at St Pancras FCC entrance who would not let me through at all, claiming that my weekly does not allow me to carry on anywhere further, even City Thameslink. The only thing that I apparently can do is go back to Gravesend with that ticket.
Can someone please confirm whether I am allowed to go on to City Thameslink from STP with my weekly? If not, then why not? I could buy an all zone travelcard from Gravesend plus high speed for 98 pounds, but I don't want to do that unless I have to, since I only want to get off at City Thameslink, and as far as I'm aware it is NOT an underground station.
I have had people from National Rail, Southeastern and FCC all on this, but neither of them know a definitive answer yet (which is rather sad, how hard can it be to tell me if a ticket is valid or not)?
Can someone please confirm whether I am allowed to go on to City Thameslink from STP with my weekly? If not, then why not? I could buy an all zone travelcard from Gravesend plus high speed for 98 pounds, but I don't want to do that unless I have to, since I only want to get off at City Thameslink, and as far as I'm aware it is NOT an underground station.
I have had people from National Rail, Southeastern and FCC all on this, but neither of them know a definitive answer yet (which is rather sad, how hard can it be to tell me if a ticket is valid or not)?

It's a terribly obscure routing and something which I used to explain often to new barrier staff at Kings Cross LU station, "Whereyougoinwiththisthenguv?" or "It ain't got a cross so it ain't allowed down ere" being quite common!