Label tags are numbered sequentially according to the order in which they are created, but you can renumber them to remove gaps in a sequence, or to change the starting number or increment value.
By default, newly created tags are unique. Duplicate tags are only created manually. Specify tag starting and increment numbers in the Table Tag Numbering dialog box. You can create a duplicate by opening an existing drawing that contains duplicates across sites/alignment collections or with the renumber command. You can create or avoid duplicate tags as desired.