Where seated real estate has been heretofore or shall be hereafter returned to the county commissioners of the proper county for non-payment of taxes thereon, and has been or shall be sold in satisfaction of said taxes, the owner or owners of such real estate shall have the right to redeem the same within the same time and in the same manner as if the real estate were unseated and assessed and sold as unseated: Provided, That as to seated real estate heretofore sold such right of redemption shall not expire before the expiration of one year from the date of this act: And provided further, That no title by tax sale which shall have become absolute prior to the passage of this act shall be affected by its provisions.