I´m participating in the Herbarium "queste". So far I´ve encountered two date-stamps which I could not find in the date-range. Today was the last one, it´s date was 1889.
Maybe somebody can increase the range a little bit.
PS Of course this is not very problematic AT ALL!
Just put 1890, but in the additional notes put this is 1889! Also if you hit the discuss button when on the actual record, you can get it up in front of the scientists and they will take note.