The date of manufacture shall be determined as follows:
(a) For products for which an official standard of potency is prescribed in either Sec. 610.20 or Sec. 610.21, or which are subject to official potency tests, the date of initiation by the manufacturer of the last valid potency test.
(b) For products that are not subject to official potency tests, (1) the date of removal from animals, (2) the date of extraction, (3) the date of solution, (4) the date of cessation of growth, or (5) the date of final sterile filtration of a bulk solution, whichever is applicable. [38 FR 32056, Nov. 20, 1973, as amended at 42 FR 27582, May 31, 1977]