according to the Coast Guard site -http://www.uscg.mil/hq/cg5/cg5214/pfdselection.asp#recreational

Note: The Coast Guard is working with the PFD community to revise the classification and labeling of PFDs. When completed, this information will be updated and hopefully be somewhat easier to understand. ....

Isn't there some rule that requires a throw able on board as well?