I found a slew of Yiddish typewriters at the Yiddish Book Center (about 15), and I'm trying to date them all. The problem is sometimes these Yiddish language typewriters used previous builds, I assume in making the custom-made reverse carriage. For example, on the first one below, the decal doesn't match other 1917 models I've found online. I could be wrong. Do you see any inconsistencies to better date these?

The two serial numbers are 
Underwood #994707 (1917?)
Underwood 46T #10886375 (1918?) [the carriage is missing]