N.Y. Comp. Codes R. & Regs. Tit. 20 §§ 4-4.9
If, after exercising due diligence, the corporation does not have adequate information to use the delivery destination method, it should apportion its receipts from that service or other business activity to New York using the preceding taxable year method based on the apportionment of receipts from the sales of that type of service or other business activity for the preceding taxable year. The amount included in New York receipts for the current taxable year is determined by multiplying such receipts by a fraction, the numerator of which is the amount included in New York receipts from the sales of that type of service or other business activity in the preceding taxable year and the denominator of which is the amount included in everywhere receipts from all such sales of that type of service or other business activity in the preceding taxable year. This method of the hierarchy cannot apply in a corporation's first taxable year. A corporation that cannot use this method must apportion the receipt using the current taxable year method (see section 4-4.10 of this Subpart).
N.Y. Comp. Codes R. & Regs. Tit. 20 §§ 4-4.9