Mass. Gen. Laws ch. 245, § 9

A person not concluded by a judgment for the commonwealth under the preceding section may, until his claim is barred by law for the limitation of real actions or otherwise, bring an action to recover the land from the commonwealth or from any person then holding under it. He may deny and disprove any facts alleged and proved in the first action and allege and prove other facts in support of his claim and shall, if it appears that he is entitled to the land, have judgment and execution therefor.