Applying a retention date on a file will ensure that:

A.
data cannot be read until the date is set.

B.
data will not be deleted before that date.

C.
backup copies are not retained after that date.

D.
datasets having the same name are differentiated.

Explanation:
A retention date will ensure that a file cannot be overwritten before that date has passed. The retention date will not affect the ability to read the file. Backup copies would be expected to have a different retention date and therefore may be retained after the file has been overwritten. The creation date, not the retention date, will differentiate files with the same name.