When the date of publication is not found on the resource itself, you can indicate that in an RDA record with a statement like [Date of publication not identified] (RDA 2.8.2.6), but it is more helpful to supply a probable date or date range if you can. These are recorded in brackets with phrases like the ones in RDA 1.9.2:
[2014] [2010?] [1951 or 1952] [between 1940 and 1980] [not after 1600] [not before 1982]
AACR2 (1.4F7) allowed the [between 1981 and 1993] construction, but only for dates fewer than 20 years apart.
