Punctuation in X82 fields:

The punctuation of the subelements of a heading is generally dictated by subject heading system/thesaurus rules.  These input conventions clarify MARC punctuation practices.

An X82 field does not end with a mark of punctuation unless the field ends with an abbreviation, an initialism, or data that ends with a mark of punctuation.

Examples:

182  ##  $yTo 221 B.C.

182  ##  $y1981-