Keep track of which tabs you've created before, and only create tabs for names you haven't already seen.
If you're selecting the manager names from an SQL query, then use DISTINCT
so you get a list of unique values.
You could add all the manager names to a TStringList
with Sorted = True
and Duplicates = dupIgnore
. Once you've added all the names, you can read back the contents of the list, and it will be free of duplicates.