N.H. Rev. Stat. Ann. § 515:5

If, upon the trial of the issues upon such pleadings, either party maintains by his evidence such of the matters by him pleaded as would constitute an answer to or avoidance of the matters pleaded by the other party such issue shall be considered to be maintained by the party producing such evidence, notwithstanding other matters alleged in his pleadings may not be sustained by the proof.