Is it too late to seek Rule 11 sanctions?

As every North Carolina litigator should know, Rule 11 of the Rules of Civil Procedure states that, by signing a pleading or “other paper” (motion, subpoena, etc.) related to the litigation, the attorney certifies that,

to the best of his knowledge, information, and belief formed after reasonable inquiry it is well grounded in fact and is warranted by existing law or a good faith argument for the extension, modification, or reversal of existing law, and that it is not interposed for any improper purpose, such as to harass or to cause unnecessary delay or needless increase in the cost of litigation.