[itimpi]

The default action in Calibre if a library does not already exist at the new location is to move the previous one to this location which sounds like what has happened?

If you had first copied the old library at the OS level then you would have two libraries ( which are initially the same but can now start deviating) which you can now switch between. Alternatively you could have used the Calibre command that creates a new empty library at the new location.