N.H. Rev. Stat. § 477:16
When any instrument of writing shall have been on record in the office of the register of deeds in the proper county for the period of 10 years, and there is a defect in such instrument because it omitted to state any consideration therefor, because it was not acknowledged, because it was not validly acknowledged, because it was not witnessed, or because it was not sealed, such instrument shall, from and after the expiration of 10 years from the filing thereof for record, be valid as though such instrument had in the first instance stated the consideration therefor or had been acknowledged, witnessed, or sealed in full compliance with the requirements of law. Such instrument shall, after the expiration of 10 years from the filing of the same for record, impart to subsequent purchasers, incumbrancers, and all other persons whomsoever, notice of such instrument of writing so far as and to the same extent that such instrument then is recorded, copied, or noted in such books of record, notwithstanding such defect. Nothing in this section shall be construed to affect any rights acquired by grantees, assignees, or incumbrancers after the filing of such instrument for record and before the expiration of 10 years from the filing of such instrument for record.
RSA 477:16
1949, 191:1. RSA 477:16. 1963, 65:1. 1967, 20:1. 1977, 366:6. 1981, 303:3. 1985, 91:1, eff. Jan. 1, 1986.