You misquoted the law. There’s no period after “in any one year”.

> Section 3. Subject to the provisions of section three A and except as otherwise provided in this section and in section ten, a motor vehicle or trailer owned by a non-resident who has complied with the laws relative to motor vehicles and trailers, and the registration and operation thereof, of the state or country of registration, may be operated on the ways of this commonwealth without registration under this chapter, to the extent, as to length of time of operation and otherwise, that, as finally determined by the registrar, the state or country of registration grants substantially similar privileges in the case of motor vehicles and trailers duly registered under the laws and owned by residents of this commonwealth; provided, that no motor vehicle or trailer shall be so operated on more than thirty days in the aggregate in any one year or, in any case where the owner thereof acquires a regular place of abode or business or employment within the commonwealth, beyond a period of thirty days after the acquisition thereof, except during such time as the owner thereof maintains in full force a policy of liability insurance providing indemnity for or protection to him, and to any person responsible for the operation of such motor vehicle or trailer with his express or implied consent, against loss by reason of the liability to pay damages to others for bodily injuries, including death at any time resulting therefrom, caused by such motor vehicle or trailer, at least to the amount or limits required in a motor vehicle liability policy as defined in section thirty-four A.