Section 140.510 - Form not to affect validity - presumption of validity1. No tax authorized by the laws of this state, and which shall be assessed on any property within this state by any officer authorized to make assessments shall be held to be illegal or invalid for want of any matter of form in any proceeding not affecting the merits of the case, and which shall not prejudice the rights of the party assessed.2. And all taxes assessed upon any property in this state shall be presumed to be legally assessed until the contrary is affirmatively shown, and no sale of real estate for the nonpayment of the taxes thereon shall be rendered invalid by showing that any certificate, return, affidavit or other paper required to be made and filed in any office is not found in any office where the same ought to be filed or found, but until the contrary is proven the presumption shall be in all cases that such certificate, return, affidavit or other paper was properly made and filed in the proper office.