If a cooperative school district was organized prior to July 1, 1963, the basis for the apportionment of all such costs may be subject to review, pursuant to an article for that purpose duly inserted in the warrant for a district meeting to be held at any time after the expiration of the 5-year period measured from the date of the first annual meeting. If the apportionment formula for a cooperative school district has been duly changed, or if an article to continue the current formula has been passed at a district meeting, the basis for the apportionment of all such costs may be subject to review, pursuant to an article for that purpose duly inserted in the warrant for a district meeting to be held at any time after the expiration of the 5-year period measured from the date of the meeting at which the last change was made to the cost apportionment formula or the last article to continue the current formula was passed. In either case, the cooperative school district may then by majority vote elect to apportion all such costs by the adoption of one of the formulas set forth in N.H. Rev. Stat. § 195:7, I(a), (b), or (c). Such apportionment may be reviewed in the same manner at any time in order to permit the enlargement of the territory of a school district or an increase in the number of grades for which the district shall be responsible.