What you have written makes no sense at all.
Where are you seeing the 'tables'?
If you open attempt to add a data source to a Word mail merge, by default it
will seek that data source in the 'My Data Sources' folder. This folder like
any other folder can contain a variety of files.
Maybe http://www.gmayor.com/mail_merge_labels_with_word_xp.htm  will help by
giving you an overview of mail merge?

It sounds as if you are creating each new mail merge data source in the same
Excel workbook. If so, you will have multiple Excel worksheets in that
workbook and you will see one "tab" for each worksheet near the bottom of
the Excel window when you have the workbook open.

When you try to open the workbook in Word as a data source, Word lists all
the worksheets in the workbook.

If that is what is happening, what you should probably do is
a. start creating each new merge data source in a new Excel workbook in
your My Data Sources folder (or wherever you want)
b. when you have finished using that Excel workbook, move it out of the My
Data Sources" folder so that it is no longer available for selection, or
delete it if you really do not need it any more.

If you want to tidy up your existing workbook, you can right-click on each
worksheet's tab and delete that sheet. If you need to keep the data, you can
export the sheet's data first.

Peter Jamieson