There's another possibility, that I even feel silly to bring up, because it was something that happened on the old days when TAR had more budget, like the old days of 13 legs per cycle, even though I really feel its is unlikely - which is a simplified version of the two destination finale, that was something that used to happen up between Season 5 to Season 10. Colin & Christie are the only vets ever to experience this, cause from S11, it was back to a single destination in the finale. That would even allow for a F4 finale if they chose to try it again, with 4th place eliminated before heading to end-city.
I bring this up cause I was re-watching TAR5 over the weekend, and the only challenge set in final city were the final puzzle / maze challenge, as there was another city also part of the final leg.