I try to purchase certified Angus beef (CAB). I ask the butcher for the date on the case box. That is one day after the kill date. I keep the briskets in the original cryo packaging. Do not open, do not fold, spindle or mutilate. Keeping it sealed is an absolute.
I place the meat package into brown paper bags to protect from light. I put in the refrigerator in the garage, which is rarely opened and I keep at 36-38 degrees. You must maintain less than 40 and over 32 degrees.
I keep for 35-40 days. Some say 28 days is perfect others 50 days. I do not like to go over 40 days. I did have one failure. When I open the package there is no odor. If there is an odor, then consider throwing it away, it may have gone bad.
When I use it, I use Butcher's marinade and inject the brisket about 6 hours prior to cooking. (Check out product at Butcherbbq.com.)
I have done very well with this product. (8th, 5th, 3rd and a 1st) (87 at the royal, oh well)
Yours in Q