I did get to 1930s in the American scenarios, even I play the game until 1990s, I did not see the Challenger. For the European scenario, the latest starting year for the Europe map is 1870s. Since the game design limit the players running a railroad for 100 year only, I reach endgame in 1970 and can never play till 1972. Also, RE Class 6/6 never appeared before 1970.