After speaking to several different service persons at Kellogg's, the consensus seems to be that you must postmark the Nov. 30 '01 by Nov. 30 of this year. All the service reps said that the '01 expiration date marked certificates would be rejected, in spite of the currently available certs. with the same p.o. box, that expire Nov. 30 of '02. I won't take any chances, though that rule seems a bit odd.
Also, they all said that you may mix the different certificates. Just send all your certificates to the p.o. box listed on the certificates that you have the most of.