In 1975 the TT Class ferry holds are introduced, but I can't find a ship they'd fit on. Presumably there is something missing.
Thank you for spotting that: the problem is actually with the introduction dates: the holds have introduction and retirement dates in January of 1975 and 1992, whereas the vessel itself has an introduction date in November 1975 and a retirement date of September 1992. I have now updated the holds to match the vessel. In the meantime, you should be able to use the ferry in November in your game.