The separate accounting requirements contained in subparagraphs (1), (2), and (3) of this paragraph (b), are applicable, in the case of the taxes described in paragraph (a)(1) of this section, to taxes with respect to wages or compensation paid after receipt of the notice from the district director, irrespective of whether such wages or compensation was earned prior to or after receipt of the notice; and, in the case of the taxes described in paragraph (a)(2) of this section, to taxes with respect to taxable payments made after receipt of the notice from the district director, irrespective of whether the transactions with respect to which such payments were made occurred prior to or after receipt of the notice.
26 C.F.R. §301.7512-1