The TSB makes reference to the allocation that the IT 203-B does. The only hard part would be how to determine since they are not solely dealing with one year.

Section 132.18 (a) of the Regulations provides, in part:
(a) If a nonresident employee (including corporate officers, but excluding employees
provided for in section 132.17 of this Part) performs services for his employer both within and
without New York State, his income derived from New York State sources includes that
proportion of his total compensation for services rendered as an employee which the total
number of working days employed within New York State bears to the total number of working
days employed both within and without New York State.