I have two blocks from 1923. One is July and the other is December. The casting boss where the numbers are stamped is different between the two. The earlier one cuts back under itself while the later one goes straight all the way down to the water inlet section. I think I have seen these interchangeable for several years. Or was there a cut off date?
Also, were the numbers always 1/4" high ... or did the factory use other sizes?