The total number of officers authorized by law to be on the lineal list during a fiscal year may be temporarily exceeded if the average number on that list during that fiscal year does not exceed the authorized number.
33 U.S. Code § 3004 - Strength and distribution in grade
(a) GradesThe commissioned grades in the commissioned officer corps of the Administration are the following, in relative rank with officers of the Navy:
Lieutenant (junior grade).
(b) Grade distribution
(c) Annual computation of number in grade
(1) In general
(2) Method of computation
(d) Temporary increase in numbers
(e) Positions of importance and responsibility
(f) Preservation of grade and pay