I think it is the years of service that matter, so long as the member has at least 50 points a year:
"a) Except as provided in subsection (b), for the purpose of determining whether a person is entitled to retired pay under section
12731 of this title, the person’s years of service are computed by adding the following:...
(2) Each one-year period, after July 1, 1949,
in which the person has been credited with at least 50 points on the following basis: (A) One point for each day of— (i) active service; or
(ii) full-time service under sections
316,
502,
503,
504, and
505 of title
32 while performing annual training duty or while attending a prescribed course of instruction at a school designated as a service school by law or by the Secretary concerned;
if that service conformed to required standards and qualifications.
(B) One point for each attendance at a drill or period of equivalent instruction that was prescribed for that year by the Secretary concerned and conformed to the requirements prescribed by law, including attendance under section
502 of title
32.
(C) Points at the rate of 15 a year for membership— (i) in a reserve component of an armed force,
(ii) in the Army or the Air Force without component, or
(iii) in any other category covered by subsection (a)(1) except a regular component.
(D) Points credited for the year under section
2126 (b) of this title.
(E) One point for each day on which funeral honors duty is performed for at least two hours under section
12503 of this title or section
115 of title
32, unless the duty is performed while in a status for which credit is provided under another subparagraph of this paragraph.
For the purpose of clauses (A), (B), (C), (D), and (E), service in the National Guard shall be treated as if it were service in a reserve component, if the person concerned was later appointed in the National Guard of the United States, the Army National Guard of the United States, the Air National Guard of the United States, or as a Reserve of the Army or the Air Force, and served continuously in the National Guard from the date of his Federal recognition to the date of that appointment.
(3) The person’s years of active service in the Commissioned Corps of the Public Health Service.
(4) The person’s years of active commissioned service in the National Oceanic and Atmospheric Administration (including active commissioned service in the Environmental Science Services Administration and in the Coast and Geodetic Survey). "
I would think that the years of creditable service takes this into account, but I would look at if he has at least 50 points a year...my hunch is that with all the breaks/changes in service, he may have some years with less points than he would have if he drilled every month, did AT, etc., but may have 50 or more points. Does that capture the difference? My main thought is that if he gets a 20 year letter, he will be good (not that that is the deciding factor, if he is otherwise qualified, but it is good evidence that he has met the standard). My other question is does he have a choice, or is he being referred now to an MEB? Obviously, if he has a choice, he should wait till 20 years. But, if he does not have a choice, the point is moot, unless he can drag things out till 20.
Hope this helped.