There are a few community improvements that are language extensions. The standard had no notion of multithreading, MOP was not in the standard, and packages really needed some way to avoid collisions of short package names (which lead to the de facto standardized package local nicknames.) Pathnames may also have seen some de facto standardization; they were poorly specified in the standard.
ANSI CL was last ratified in 1994; there has been no standard language change, and the community language improvements are just macro libraries. You should be able to take your alexandria utilities library, or optima pattern matching or whatever back to 1995.