Circa 1911-12 - As seen with the Newark Cars  we can assume the cars with PENNSYLVANIA markings are earlier than the cars with THE IVES RAILWAY LINES markings, but with the 56 caboose the differences are not as clear. It would appear that Ives went back to the PENNSYLVANIA markings sometime after 1915 and actually the cars with THE IVES RAILWAY LINES markings are harder to find.

Comparison of two early  56 Caboose - side (above) and ends (below) note that the Pennsylvania caboose has green doors and windows, while the IVES Caboose has red doors and windows. Note also the lettering on the ends PA. R.R. and I.R.L. The early caboose is unique in that "THE IVES RAILWAY LINES" version is much harder to find. On the other hand the version with the green windows and doors is also hard to find.