There's been some fakes going about recently, check WEDINOS.
My advice to you is send one of the MSJ's you have off to WEDINOS to see if it's legit or fake. There's been fakes with ultra-potent RC benzos like flubromazolam which is a nasty surprise if you're expecting 10mg diaz.
Regarding the deaths most do not come from the MSJ's themselves, but rather from mixing them with heroin and other opiates. Any benzo + opiate combo is potentially lethal too so it's not exclusive to the MSJ's and it's good HR advise to avoid such combos.
But as I said, with fakes known to be doing the rounds I do suggest sending one to WEDINOS to see what you have. After all their tests are free and only take a few days. All you need to do is fill out a form.