I don’t have any hard numbers. My statement was based on 3 things. First, lots of conversation with Richard Hendrickson about appropriate tank cars, where he pretty unequivocally said that the GATC type 30 was the most important fleet need for General American for my era (1944) and obviously subsequent to that. Second, that the type 17 design was obsolete by the 1930s, although examples certainly can be found much later. Third, casual (and I stress that this is casual) observation of photos of WWII era tank car trains shows a few type 17 cars, with a good number of type 30 cars. I tend not to rely on individual car photos because cars can be misrepresented in frequency due to their “oddness”. 

As was noted on the list, hard numbers are generally not available, unless you have been able to find some, in which case, please share! :) 

I was wondering what the production numbers of each series were. Do you happen to know that? To be honest, I wouldn’t be surprised if the production of the type 17 exceeded the type 30-like cars, but the question would be, 20-30 years after they were built, what numbers remained?

And, of course, I have oversimplified, because with all of the acquisitions, as well as construction changes at GATC, cars in the GATX pool are really a “dog’s breakfast of styles, probably with no one car reaching 50% of the fleet.