The cvs rtag command tags the repository as of a certain date or time (or can be used to tag the latest revision). rtag works directly on the repository contents (it requires no prior checkout and does not look for a working directory).
The following options specify which date or revision to tag. See the section called “Common command options”, for a complete description of them.
dateTag the most recent revision no later than
date.
Only useful with the -D
date or -r
tag flags. If no matching revision is
found, use the most recent revision (instead of ignoring the
file).
tagOnly tag those files that contain existing tag
tag.
The cvs tag command also allows one to specify files by revision or date, using the same -r, -D, and -f options. However, this feature is probably not what you want. The reason is that cvs tag chooses which files to tag based on the files that exist in the working directory, rather than the files which existed as of the given tag/date. Therefore, you are generally better off using cvs rtag. The exceptions might be cases like:
cvs tag -r 1.4 backend.c