dating a ports tree

[Scott K. Benolkin]

For CVSuping a ports tree (e.g., the ports distribution from a release CD)
for the first time (i.e., no preexisting checkouts file), section 4.3 of
Salvo Bartolotta's "CVSup Advanced Points" article
(http://www.freebsd.org/doc/en_US.ISO8859-1/articles/cvsup-advanced/article
.html)
recommends, "you should specify a date as close as possible to that of
`shipping' of your ports tree."  It's easy enough to do this roughly, but
I'm curious if anyone knows an "official" (or at least surefire) way to
easily and precisely determine the "shipping" date of a ports tree
(realizing that the "date" keyword will specify a time down to the second).
 I'm not trying to say this is essential, but if there's a best practice,
I'd like to know.

Please CC to my address.  Thank you for your time and knowledge/cleverness.

Scott

-- 
"Frederick, is God dead?" --Sojourner Truth