Bachmann's original Amfleet coach dates back to the late 60s / early 70s and was probably designed for use with their Budd Metroliner locomotive. Said coach model was slightly revised circa 1997 (the noteworthy change being the addition of interior lighting). It was then completely redesigned circa 2007 (and with a cafe car entering the mix at the same time). I'm told that the pickup scheme on the lit cars (vis'a'vis the wheels) creates quite a bit of drag, requiring one heck of a lot of motive power to pull even a moderately sized train around.
Coach (first and second version, catalog #72xxx) -
Coach (third version, catalog #14xxx) -
To identify a given car, just look on the bottom. The first version is stamped "Bachmann Hong Kong", the second version is stamped "Bachmann China", and the third version is stamped with the round Bachmann logo -