There are some competitive BBQers who wet age their briskets in the Cryovac in the fridge for several weeks. A while back on The BBQ Forum, I read that one competitor wet-aged his briskets for as long as 45 days from the date of packing printed on the case box.
In the book "The Complete Meat Cookbook", the authors mention 36*F as a target storage temp. They write, "This form of aging will help to tenderize the meat by the same enzymatic processes involved in dry-aging. But because wet-aging involves no loss of moisture through evaporation, the flavors do not become concentrated as they do with dry-aging."
In answer to HJP's question, yes, all beef is wet-aged to some extent, from the time it's Cryovaced until the time it is removed from the Cryovac. Again from the aforementioned book, "Most meat we purchase these days is not deliberately aged. It will most likely be 4 to 10 days old, depending on how fast the shop turns its inventory and how long it takes to get from the packing house to the meat case."
That may be true at a place like Costco, but my guess is that much of the meat I see at a place like Cash & Carry is certainly more than 10 days old.
Regards,
Chris