The 1890 maker's country stamp does not work Absolutley..
If it has a stamp it is "Probably" post 1890 and was exported, now if the razor was made post 1890 but not exported it doesn't have to have a stamp..
There are also early razors that have Country stamps, maybe just because they were proud of the razor..
As usual there are no real "Carved in Stone" rules in this sport