One quick thing . . . . to properly wet age meat the temp must be between 35 and 39 degrees. Over 39 and you're unsafe. Under 35 and instead of aging, you're "prolonging" the product. Yes, you're aging it, but at a slower rate yet, and the range you can age at this temperatures gets muddy.
You MUST know the kill date to wet age brisket. DO NOT rely on a "sell by" date. If you don't know the date, don't do it. When you do open that seldom used, almost dedicated refrigerator where you stash your competition briskets for aging, glance at the briskets. When the gas bubbles are about dime size, you're usually about 30 days old. When they get to be nickle size, you're usually about 40 days old. When they get to quarter size, it's time to cook that brisket. I only mention the size of the bubbles because sometimes they appear before the days I reference. Properly tracking the days is the best reference for aging brisket, but watching what is happening in the package will save you from throwing away briskets. If the bubbles get bigger, you can be in trouble. You will then have to rely on an inspection with your nose when you open the packaging.
Also, there will be a "smell" when you open a 40 - 50 day old properly wet aged brisket. It will be a non offensive musky beefy smell that will dissipate in roughly four or five minutes. If there is any sharp or sour smell to the brisket, it's bad. You will absolutely know the difference. Please do not talk yourself into cooking a brisket that has a sharp sour smell no matter how faint. It's bad, plain and simple. It's not worth the risk.
Sorry this turned into several comments. I have aged briskets for about six years now. In all of that time, I have only had one bad brisket and there were circumstances out of the norm that told me it could be bad.
If I do everything half ass, how can I be a "full fledged" anything?