Wwweeelll if we include the "offical launch" of TC then it is around since march 20, 2013 if you want to have the exact date and based on the announcments i could find on the offical website.
So you can technically say that TC is the currently "longest system with it´s story" after the catastrophic first try and the new re-release that was planed for June 12, 2018 but due of a required delay did happen one week later on June 19, 2018.
So you can say it took TC 5 years and 2 months to be released for real and since then then they have brought at least 1 part every year so 2022 seems to be fitting in the end for TC4.
If we want to go really crazy (and consider Sirius not as a "real system due the lack of storymissions" it gets even more cus Sirius was released the first time on November 04, 2011 what means already 1 year and 4 months between Siris and TC that could have been completed wwwaaayyy sooner if the planed "Episodes driven by the players voting" would have gone more smoothly and we may even be 2 or even 3 system further then currently
.
But the time of nearly 5 years is the only reason why we still sit in TC