See your Compilation vs. Collaboration Decision Tree, Charts #1-2, on the Cornell RDA wiki at:
https://confluence.cornell.edu/x/uoNECg
Conventional collective titles are used in RDA under 6.2.2.10 for compilations that have single creators. This includes the complete works of a person, family or corporate body and the complete works in a single form of a person, family or corporate body.
In addition, the LCPS for RDA 6.2.2.10.3 on compilations of two or more works that are not complete works or complete works in a single form directs:
Instead of recording the preferred title for each of the works in the compilation, record a conventional collective title followed by "Selections."
QUESTION: Suppose you have a situation where you want to use the conventional collective title in the form |a Author. |t Essays. |k Selections. You do a name/title authority search and discover that LC has already established this exact name/title combination under AACR2. Are you allowed to use this name/title combination on your new RDA bib as well?
ANSWER: Yes! Go right ahead and use it without a qualifier.
The instructions at 6.27, which make it sound like perhaps you should qualify your name/title with an element to make it unique, are meant to help you distinguish one work from another. But by using the conventional collective title, you have decided that you are not distinguishing between works. According to Dave Reser at LC, "by applying 6.2.2.10 and using a conventional collective title, you are essentially saying that this is the title of the collective work in as many combinations as may be found, and you do not need to distinguish it at the work level. The resulting authority record may thus represent one or more different groupings of "selections" in reality."
"We find," Dave continues, "that distinguishing at the work level really boils down to situations where the creator has issued different works under the same title (rarely happens, but does happen) and more likely the situation where no creator is used to construct the authorized access point representing the work" (as in serials).
"That said," he continues, "it is possible to distinguish different expressions following 6.27.3. LC does so only in the limited cases identified in the LCPS for 6.27.3, including use of the conventional collective titles that begin with "Works."