No unit comes with a map card unless it is a special sale NAV edition.

You can use Navionics or Lakemaster mapping with the software your unit has. You were "told" BS.

1.640 has nothing to do with getting to 1.900 other than having previous software that has the Humminbird Basemap install software from an older version than 1.640. The Basemap software is 1.460. Then you would also need the separate Basemap file to install after that.

What is the whole model name of your unit? Software is unit specific and not interchangeable between any models.
The model name is in the SYSTEM STATUS view.