I'm afraid the icon still isn't appearing on my save files, unless I'm doing something wrong :(. Would you mind if I were to send a message on Discord with some more specifics? So sorry for this bother! >.<
Whether the icon is appearing or not, if you go to the very beginning of the game before the route split down to that lock, the choice should appear, as long as you are on the file that is marked with a "TBC". If you don't have a file with "TBC", you simply have to autofill onto a specific segment (at the exact rightmost one you've played through already) and it should work.