I am far from an expert on fare rules, but IME most non-refundable fares have an "N" somewhere in the fare basis. Looking at a fare search using one of sbm12's tools (sorry, don't know how to post the results properly), I see the following fare bases for a dummy CLE-MBJ search in mid-March:

GHWNTN
GHXNTN
ULX7CRB
ULW7CRB
KLX3CRB
KLW3CRB
BLX0CRB
BLW0CRB
ZA7N
BOX
ZR3N
YOX
ZR0N
ZOX
DOX
COX

I would conclude from this that there are several non-refundable G, U, K, B, and Z fares, and that BOX, YOX, ZOX, DOX, and COX represent refundable fares. I would also conclude that Dr. Seuss's ghost works for CO setting fare buckets.

Also, IME, the fare rules of non-refundable fares usually specify that the fare is non-refundable, whereas the fare rules of refundable fares usually don't mention refunds.

Will you be able to support a B-UP for a trip after status expires?