(a) Prepaid subscription income to which section 455 applies shall be included in gross income for the taxable years during which the liability to which the income relates is discharged or is deemed to be discharged on the basis of the taxpayer's experience.

(b) For purposes of determining the period or periods over which the liability of the taxpayer extends, and for purposes of allocating prepaid subscription income to such periods, the taxpayer may aggregate similar transactions during the taxable year in any reasonable manner, provided the method of aggregation and allocation is consistently followed.