Some collectors marvel at finding a tin piece that has something else printed inside. It is not all that uncommon. Marx, like any manufacturer, wasted nothing they could use. In the late prewar period Marx was trying to churn out every train set possible from existing stock. New sheet metal was not available. However, unused litho sheets could be relithographed on the opposite side and pressed into cars needed to complete train sets. This caboose had been intended to be a red stripe litho tender!

In my collection I have a double deep box set that is made almost entirely from over-litho'd stock. The engine never had a stack or bell. The black wedge tender is copper underneath. All of the six-inch cars have frames made from blacked out car bodies. The set included a ramp car but no load for it (dang!). Instead there are two six-inch pressed steel trucks. Another collector has the identical set!