When rebuilding the aliases files, each database is opened before it is rebuilt or not. The -d38.4 debugging switch shows the success or failure of each open:

map_init(dbtype:name, file, pass)   from -d38.2
     dbtype:name file  valid or  invalid 

The status is valid if the open succeeded; otherwise, it is invalid.

The -d38.4 debugging switch also shows each map being looked up in a switch database type (switch):

switch_map_open(name, file, mode)   from -d38.2
        map_stack[index] = dbtype:name  

If the name was not declared in a K configuration command, the following error is printed:

Switch map dbtype: unknown member map name