ALC did have presses with a 19" track. Specifically Hoe company number 5 presses. BUT and this is an important thing. ALC was a huge printing concern, the info about the presses comes from a diagram of one floor of the plant in an article about their conversion to electricity to run the machines.(Or use of electricity in the plant when it was new- I don't recall which it was. ) That was in Scientific American back then.
Most huge printing companies will have a variety of presses. The only places I've seen with only one size press have been either very small like someone running one of the little 10" presses in their garage. Or a place that only prints one fairly consistent item, like a newspaper or book publisher.
One of the things I find fascinating is that compelling arguments can be made for Both multiples of 12 and multiples of 17.
I will also say that I've seen the breakdown Chris did of the 460 series, and being at the time more in the 12 camp than the 17 I tried to use pop report numbers to break his groups. With the exception of maybe 4 cards that looked like they belonged in a different group my attempt at proving those groups wrong failed. And the very few that could have moved groups came in pairs - If one had too many graded copies for it's group it matched another group very well, AND that other group had a card that matched the other group. Neither of the swaps broke the overall pattern by requiring an unconfirmed combination.
Since then I've become convinced that both 12 and 17 are correct for particular portions of some series.
Some quick math based on a couple decent guesses and using Scot Readers estimates of how many might have been printed also leads me to believe that at least for the very common backs more than one press was used at a time. The numbers indicate a need for almost constant printing of Piedmont for sure. Say 100 million P350s? At 17x6 - 102 per sheet, that's 980392 sheets. Times 9 impressions/sheet is 8823529 impressions. At 800/hour = 11,029 hours. (And that doesn't count setup time and pre production, and cutting/packing) A 50 hour workweek is only 2600 hours a year. Three shifts with no downtime? 459 days
Use of a two color press would cut the time in half. Using multiple presses would make it manageable.
Another option would be a far larger sheet, perhaps made up of 4 smaller sheets. Many US stamps were printed this way. Press sheet =4 10x10 panes that were then cut apart before perforating.
Steve B