With few exceptions, chronological subdivisions are enumerated in the subject headings list. The heading with the chronological subdivision which most closely covers the period treated in the work is assigned. Few chronological subdivisions are free-floating. Under headings governed by pattern headings, chronological subdivisions are free-floating and can therefore be transferred to other headings in the same category as appropriate.

25.4 Reference

See also:

25.0 Use of subdivisions