From and after the passage of this act, assessors, supervisors, and collectors of road and school taxes, be and they are hereby required to make their returns for the collection of all taxes on unseated lands on or before the first day of January in each and every year, and if not so made by said assessors and collectors, such returns shall not thereafter be received, nor shall such taxes be a lien on real estate: Provided, That this section shall not be construed to exempt any such assessors and collectors, and their bail, from liability for not making their returns according to law.