Where any assessment to tax, or any duplicate of assessment to tax, or any return or other document relating to tax, has been lost or destroyed, or been so defaced or damaged as to be illegible or otherwise useless, the Commissioners, inspectors, collectors and other officers having powers in relation to tax may, notwithstanding anything in any enactment to the contrary, do all such acts and things as they might have done, and all acts and things done under or in pursuance of this section shall be as valid and effectual for all purposes as they would have been, if the assessment or duplicate of assessment had not been made, or the return or other document had not been made or furnished or required to be made or furnished:

Provided that, where any person who is charged with tax in consequence or by virtue of any act or thing done under or in pursuance of this section proves to the satisfaction of the Commissioners having jurisdiction in the case that he has already paid any tax for the same chargeable period in respect of the subject matter and on the account in respect of and on which he is so charged, relief shall be given to the extent to which the liability of that person has been discharged by the payment so made either by abatement from the charge or by repayment, as the case may require.

In this section, "the Commissioners " means, as the case may require, either the Board or the General or Special Commissioners concerned.