MTH's center beam flatcars were made in both open truss and opera window versions; below are the catalog numbers and year announced for the Premier version with opera windows:
20-98230 - Tobacco Valley Lumber (1999)
20-90014B - Burlington Northern (2000)
20-98307 - Burlington Northern (2002)
20-98308 - Hampton Lumber Sales (2002)
20-98306 - BC Rail (2002)
20-98309 - Milwaukee Road (2002)
20-98848 - CSX (Uncatalogued circa 2012; shown in image above)
20-98849 - Burlington Northern (Uncatalogued circa 2012)
20-98850 - Southern (2012)
20-95127 - Milwaukee Road (2015)
20-95130 - British Columbia (2015)
Depending on the catalog number the car will have either a simulated log load, or a simulated load of wrapped building materials such as lumber or sheetrock.
Early models have trucks which are spaced too far apart; MTH revised the tooling around 2010 and moved the trucks to a more prototypical position. The later models also feature the redesigned couplers with hidden uncoupling tabs and added brake line detail.
Hope this helps!
-John