Mont. Code Ann. § 7-12-4168

Whenever an owner or owners of lots and lands fronting on a street have done or do any work, excepting grading, on the street in front of a block at the owner's expense and the city council or commission subsequently orders any work to be done of the same class in front of the same block, the work done at the expense of the owner or owners must be excepted from the order ordering work to be done, if the work done at the expense of the owner or owners is upon the official grade and in condition satisfactory to the city engineer at the time that the order is passed.