Per another post, what probably happened is you changed the style of one tag to a standard style, and Civil3d was kind enough to remember that you were using that tag for that label (even though you're not anymore!). So you should delete all the labels that might have had tags and relabel. Then the tags should be able to be renumbered consecutively.
-Chuck Lamping
Chuck Lamping, P.E.
Westwood Professional Services
EMAIL chuck.lamping_at_westwoodps.com
WEB www.westwoodps.com