Én olvasatomban 1997-től vannak: 

Second were the standard-design express boxcars, numbered in the 70000- 71000- and 71200-series numbers. The express boxcars were delivered in 1997, and because they lacked HEP pass-through cabling, they were restricted to rear-of-train service. 

Forrás: https://utahrails.net/pass/amtrak-mail-express.php