Ian Fairclough <[log in to unmask]> wrote:

>  Is this just legacy punctuation from earlier codes, ones that endowed
> punctuation with bibliographic significance?  Perhaps such usage is
> documented in the minutes of a committee somewhere.

Briefly looking over the old "Red Book" and AACR1 and the 1978 edition of
AACR2, the practices appear to be these:

 - if a term appears with a name in sources at hand and/or in reference
sources, then it would appear after a comma when the rules asked for the
term to be applied
 - for a term made up by a cataloger, it would appear in parentheses

As for the Other Designation element, parentheses are mentioned in LC's
response to the British Library's proposal for the element:

This is also illustrated in the minutes from the Nov. 2013 JSC meeting (see
especially pages 47-48):

Mark K. Ehlert                 Minitex
Coordinator                    University of Minnesota
Digitization, Cataloging &     15 Andersen Library
  Metadata Education (DCME)    222 21st Avenue South
Phone: 612-624-0805            Minneapolis, MN 55455-0439

  "Experience is by industry achieved // And perfected by
the swift course of time." -- Shakespeare, "Two Gentlemen
of Verona," Act I, scene iii