Their structure is quite identical, and so is their configuration in opt/otrs/Kernel/Config.pm.
Actually, for the second database, exactly the same field mapping config is used as for the first database.
In MS-SQL Server Management Studio, a display of the top 100 records shows the same field layout for both databases (apart from 1 additional field description in the second database).
Inside OTRS however, when replying to a ticket, and using the lookup function in the To: field, the records for both databases show totally different ! For the first database in correct sequence, but for the second database, not the same fields are displayed, and one field is even showing twice !
Is there any other place than Config.pm that will define how the records are displayed in a search field ?
For testing purposes, I discovered in OTRS a lovely SQL Box, which unfortunately (but I understand

Another issue, maybe a clue?, in Admin -> Customer User Management, apart from my 2 Customer User backend databases, I find in addition : "Database Backend" and "No Name 1".
Where do these originate from ?