Cvs diff --- I don't understand

[DJ Delorie]

cvs diff compares against the version your changes are based on, which
is the last version you checked out or updated to.  If you want to
bring yourself up to date wrt the latest sources, use "cvs update" and
*then* cvs diff.

In theory, you can do "cvs diff -rHEAD ..." to compare against the
latest version *instead of* the version your changes are based on, but
I've rarely used this myself.  Update/diff is the Right Thing to do.