Welcome to the message board! Very nice anniversary clock...nice dial and the columns have similar coloration. We usually compare the layout of the back plate to what is in the Repair Guide by Terwilliger. I can see that it is a full width plate, however I can't find an exact match. The closest I can see if plate 1404A which has a ca date of 1952. But I also notice that a pendulum guide cup just below the center of the pendulum is not there. The guide cup can into existence at varying times by manufacturer. The K&S you see stands for Kern and Sohne and it was reorganized in 1937. So the clock dates after that. If I had to guess, I'd say the clock is likely just after WWII, but because of the missing guide cup it could be late 1930s...doubt it was built at any time during WWII.
Hopefully a moderator can move this to the 400-day forum.
Yes, this sort of thing happens. The author did his best to locate and document all back plates but that is a very difficult task. That said, the guide is very useful. The first edition was 1953. It's been said that he did better with the clocks of his era but likely had more difficulty getting to all the designs going back 50 years or more.