Under RDA, Copyright Date is an element separate from Date of Publication and Date of Distribution. When it is recorded in the current MARC standard, it appears in its own 264 field:
264 _4 ǂc ©2014
Note that this 264 has second indicator 4 (to indicate Copyright Date Notice), the copyright symbol and date appear in subfield c, and that subfield is the only one in this field.
Copyright dates appear in many RDA records, though they are rarely technically required. RDA 2.11 says that Copyright Date is a core element if neither the Date of Publication nor the Date of Distribution is identified. That means, if you have not written anything down for date of publication or distribution, and you have a copyright date available, you must record it as such.
However, LC-PCC PS for RDA 188.8.131.52 includes instructions to supply a publication date using the copyright date when possible, if it makes sense to do so. With the publication date identified, copyright date is no longer core, so need not be recorded!
So why do all of these RDA records have copyright dates in them? I personally feel weird supplying information without indicating why, and the copyright date notice serves as a justifying note. Also, the copyright symbol is more fun to type than c was; snag my macro if you’re having trouble with it.
Even if not core, recording copyright date is allowed, and creates a fuller record. At my library, we have as policy for our RDA original cataloging that we include the copyright date notice when it was used to supply the publication date.