N.Y. Comp. Codes R. & Regs. Tit. 20 §§ 4-4.10
If, after exercising due diligence, the corporation does not have adequate information to use the preceding taxable year method to apportion the receipt, the corporation must use the current taxable year method to apportion the receipt based on the apportionment in the current taxable year of receipts from other services and other business activities that can be apportioned using the where benefit received method and the apportionment in the current taxable year of receipts from other services and other business activities using the delivery destination method. 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 all services and other business activities that can be apportioned using the where benefit received method and delivery destination method for the current taxable year and the denominator of which is the amount included in everywhere receipts from services and other business activities apportioned using the where benefit received method and delivery destination method.
N.Y. Comp. Codes R. & Regs. Tit. 20 §§ 4-4.10