No allowance of severance aid shall be made as provided in Section 41960 unless the total assessed value of taxable real property within the school district is reduced by one-half of one (0.5) percent or more during a fiscal year by reason of acquisitions giving rise to severance aid as provided in Section 41960. In determining whether or not the value of the acquisitions is equal to one-half of one (0.5) percent or more of the value of taxable real property, all of these acquisitions made during each fiscal year shall be considered as one sum.