Might as well thought in my two cents...
It was made clear in the Tangent clinic, when each car’s lettering was
slotted for. The 58 car can be back dated. Exhausting internet research was done
Friday night, many beers gave their lives for the cause. The lingering question
is: When exactly did GATC remove the stripes over/under their initials and
numbers? The consensus from those in the know in the room was 52...or
Clark, I haven't wanted to add to the (often incorrect) blather on the list about the prototypes for this model, but I can tell you, based on photo documentation, that the lines were dropped in 1945, though (of course) many cars with the pre-1945 stenciling remained in service into the early '50s and some were still around in the mid-1950s. So a minimum of back-dating on the ca. 1958 version of the model will make it correct for the late '40s and early '50s.
I got the impression from gestures at the nearby (to Tangent) “Black Cat
Decals” table that Allen would be modifying his GATX decal set for a 40s era set
for these cars. Just my impression.
Your impression is correct. That decal set will take care of us '40s modelers until Tangent does a factory-lettered GATX car with the pre-1945 lines above and below the reporting marks and numbers.
Regarding the complaints that there are other tank cars we need more while the Tangent model is just "cute," I would observe that it looks "cute" mostly because the three compartment tank car models we're used to are Athearn's ancient atrocity which scales out to about 11,000 gallons and which has absolutely no prototype. The vast majority of three compartment prototypes were of 6K gal. capacity; a few were smaller, a relatively small number were 8K, and three compartment cars as large as 10K were almost (but not quite) non-existent.
In fact, 6K three compartment tank cars were numerous in the steam/transition era (several thousand cars), many were GATC Type 30s, and they were widely used, as has already been suggested, for shipments of various grades of lubricating oil and of gasoline/kerosene/distillate/diesel fuel to smaller wholesalers. Remember, also, that not every compartment of a 6K three compartment tank car had to be full. Some shipments used only the center compartment, others only the two end compartments.
As for other prototypes that Tangent might have modeled, by far the most needed tank car models are UTLX X-3s and those are under development by another company, as David Lehlbach is well aware (as are those who were at the Friends of the Freight Car dinner on Thursday night at Naperville/Lisle). Remember, also, that the Tangent model introduces some exquisitely modeled GATC Type 30 underframe components which can easily be employed on future models with different tanks (ICC 105 Chlorine cars? 7K gal. acid cars? Not to mention 8 and 10K GATC Type 30 ICC-103s, which have never been modeled accurately except in brass).
"Cute" may be enough to sell these models to the train set bozos, especially if the models have colorful paint schemes like the Celanese model, but every prototype modeler who models ca. 1930 through the '60s and into the '70s needs at least one or two of them.