Strange World Yellow allows a form of time travel, but only to "the past." In this case, every door opens into a different new reality. Very soon after each contact, events in the world began to diverge. It was sometimes possible to buy that winning lottery ticket. Or rediscover a gold field or contract with Mark Twain when he was 16. There are Yellow worlds where the Egyptian Empire flourished and Pharaohs maintain American colonies. There are also worlds where Neanderthals never became extinct and worlds where the American Civil War was fought with lasers and nuclear zeppelins.
Doors in Yellow are typically named using three indicators: The year when discovered, the location of that reality's first door, and the number of years since discovery. For instance, "1881 Wupatki 16" means that a door first opened into the Wupatki Indian settlement when the year was 1881. This reality was first entered from the tunnels sixteen years ago and the current year there is therefore 1897.