As for Pennsylvania Tank Car, I have seen start dates of?? 1911 and 1914, both without any solid attribution.?? There are some indications that they used built-up tank bolsters on some cars, but I have never seen a confirmed PTCCo car with anything like what we are discussing here.

I compiled some info from Pennsylvania Tank Line's ORER entries the last time this topic came up:

Pennsylvania Tank Line first appears in the February 1912 ORER with a picture of PTX 1001:
https://play.google.com/books/reader?printsec=frontcover&output=reader&id=QRs6AQAAMAAJ&pg=GBS.RA1-PA522

Their entry used a picture of PTX 1061 by December 1912:
https://play.google.com/books/reader?printsec=frontcover&output=reader&id=tboMAQAAIAAJ&pg=GBS.PA998

In May 1915, the picture changed to PTX 1091. Decent picture here:
https://play.google.com/books/reader?printsec=frontcover&output=reader&id=ZPg4AQAAMAAJ&pg=GBS.RA1-PA849

The change to the "new" underframe appeared on PTX 3500 in May 1917:
https://play.google.com/books/reader?printsec=frontcover&output=reader&id=O_c4AQAAMAAJ&pg=GBS.RA1-PA915

The more familiar cast tank saddles seem to have started circa 1918.

David Thompson