The county treasurer shall each year, after receiving the tax list referred to in chapter 443, enter into the county system a notation of delinquency for each parcel on which the tax remains unpaid for any previous year. Unless the delinquent tax is so entered it shall cease to be a lien upon that parcel. To preserve the tax lien it is only necessary to enter the notation for any parcel upon which it is a lien. If the county system is such that all delinquent taxes of any preceding year are automatically brought forward against each parcel on which the tax remains unpaid for any year, the treasurer is not required to make any further entry. Any sale for a delinquent tax not noted on the county system is invalid. However, this section does not require that in order to preserve the lien of tax and make the tax sale valid, delinquent taxes must be brought forward upon the county system if the tax list is received by the treasurer less than six months preceding the date of conducting the tax sale as provided in section 446.25 or 446.28.