The following words and phrases as used in this article shall have the following meanings unless a different meaning is plainly required by the context:
Except as otherwise specifically provided in this article, service rendered on and after January first, nineteen hundred twenty-one, by a person entitled to retirement benefits for civil service employees pursuant to other laws, wholly or partly at the expense of the state or any political subdivision thereof, however, shall not constitute government service.
However, no military service shall be creditable under this paragraph two in the case of a member under an existing plan permitting retirement upon twenty years of creditable service who is receiving a federal pension (other than for disability) based upon a minimum of twenty years of full time active military service in the armed forces of the United States nor shall any military service be creditable in the case of a member under any other plan who is receiving a military pension (other than for disability) for military service in the armed forces of the United States.
N.Y. Retire. and Soc. Sec. Law § 2