Cachingsays:

One or more entity-tags, indicating one or more stored responses, can be used in an If-None-Match header field for response validation, or in an If-Match or If-Range header field for representation selection (i.e., the client is referring specifically to one or more previously obtained representations with the listed entity-tags).

Can the cache send any old entity-tag it has stored for the URL in these headers, or must it only do it for those that can beselected by the incoming request, as per the secondary cache key algorithm?

Also, this section uses "selected" in a different meaning; that should probably be changed to avoid confusion.