account in determining the reference month or reference taxable year with respect to any calendar month unless all relevant information with respect to such month or year is available to the Secretary and the Secretary has adequate time to make estimates under this section on the basis of such information before the beginning of such calendar month. (4) Treatment of insufficient information Except as otherwise provided by the Secretary— (A) if a taxpayer is not described in subparagraph (A), (B), or (C) of paragraph (1) with respect to any calendar month, the monthly advance child payment with respect to such taxpayer for such calendar month shall be treated as zero unless the Secretary determines that the Secretary can make the estimate described in subsection (b) on the basis of information known to the Secretary which the Secretary determines is reasonably reliable, and (B) if the taxpayer is not described in paragraph (1)(C) and the information on the return of tax referred to in subparagraph (A) or (B) of paragraph (1) does not establish the status of the taxpayer (in the case of a joint return, either spouse) as having a principal place of abode (determined as provided in section 32) in the United States or Puerto Rico for more than one-half of the reference month, the Secretary shall determine such status based on information known to the Secretary. (5) Transition rule In any case with respect to which section 24A was not in effect for the taxable year described in subparagraph (A), (B), or (C) of paragraph (1) (whichever is applicable), subsection (b)(1) shall be applied by substituting the qualifying children of such taxpayer for the taxable year which includes the reference month for the specified children of such taxpayer for the reference month . (e) On-Line information portal