A little more on post-trial.

What happens if any enlisted person is reduced at court-martial, or an officer who faces a grade-determination consideration, for conduct as far back as late 2000, and later retires?

10 U. S. Code 1407 sets it out for us.

(f) Exception for Enlisted Members Reduced in Grade and Officers Who Do Not Serve Satisfactorily in Highest Grade Held.—

(1) Computation based on pre-high-three rules.— In the case of a member or former member described in paragraph (2), the retired pay base or retainer pay base is determined under section 1406 of this title in the same manner as if the member or former member first became a member of a uniformed service before September 8, 1980.

(2) Affected members.— A member or former member referred to in paragraph (1) is a member or former member who by reason of conduct occurring after October 30, 2000—

(A) in the case of a member retired in an enlisted grade or transferred to the Fleet Reserve or Fleet Marine Corps Reserve, was at any time reduced in grade as the result of a court-martial sentence, nonjudicial punishment, or an administrative action, unless the member was subsequently promoted to a higher enlisted grade or appointed to a commissioned or warrant grade; and

(B) in the case of an officer, is retired in a grade lower than the highest grade in which served by reason of denial of a determination or certification under section 1370 of this title that the officer served on active duty satisfactorily in that grade.

This Rule is intended to avoid the "benefit" of the high-three rule.