The usual reasons for misalignment of labels created from the Word label function are as follows:
1. You have added a header/footer to the normal template (rename the normal template)
2. The page size set in the printer properties doesn't match the page size of the label sheet.
3. You have a scaling option set in the zoom section of the print dialog
4. Your printer has poor paper handling. Some printers will slip when faced with label stock and thus are incapable of feeding the label correctly. Cleaning the rollers in the print path may help.
If one of these is your problem then it can be quite difficult to fix later (and I am surprised that you didn't notice it before you created 200 documents).
If however you mean you want to change the label stock associated with some pre-prepared labels then see
http://www.gmayor.com/convert_labels...mail_merge.htm and
Mailmerge with Word 2007/2010