Dmytro,

1. Mettlach is the only firm that identified a year of manufacture.
2. Except for some porcelain character steins, like Bohne and Schierholz, I am not aware of old porcelain catalogs by manufacturer.
3. You might date a mold by the number, but the stein could have been made any date thereafter.
4. You might be able to say circa 1900, but you can’t say if it was before or after 1900.