Mass. Gen. Laws ch. 231, § 43: Late endorsement of pleading or process

Section 43. If a plaintiff, not an inhabitant of the commonwealth, fails, by accident, mistake or inadvertence, to have his pleading or process endorsed as required by the preceding section, the court may at any stage of the case, upon terms, allow him to procure an endorser with the same effect as if the pleading or process had been endorsed before the filing or entry thereof.