Well I think the plan for them to have everything done in 2020 is realistic.
Jacob, thanks for the response. I agree with your mention of "same class/ship" manufacturing efficiencies but only up to a point. You speak to efficiencies in the design phase, but in the end meeting schedule comes down to production resources. We really don't know how much capacity Trumpeter has in terms of their large size injection molding equipment capable of producing accurate and detailed 1/350 ship model parts. Unless they plan to retire some kits currently in production, it is hard for me, just personal opinion, to see all 23 releases complete by 12/2020.
As to design efficiencies, Littorio described well in his post above some of the significant differences in the county class that will affect the molds. I add that HMS Kent was the only one of the class to have a stern walk. As to the Austro-Hungarian battleships, first & fourth (last of class), there are major differences: 4 screws vs 2 screws affects hull parts, Szent Istvan unlike Viribus, had a searchlight platform that extended from the bridge to second funnel, and had a much larger vent square vs. round cowl forward of its mainmast. I'm not saying that are no design efficiencies to be gained but just that there is still much uniqueness to be dealt with. And as others have mentioned, given modifications and rebuilds, other variations can creep into parts you might think would be common and reusable, given the year the model is suppose to represent
As to what one sees at a show, that can be just a cleaned up test shot using prototype molds - actual volume production of a quality finished kit may still be far to the right on the time line.
I'll post later about some more about the interesting differences with classes and between difference years of the same ship for those warships mentioned in the Trumpeter catalog. The three Dido class AA cruisers are interesting choices in terms of spanning the range of variations that class saw.