Also for reference, glycin powder is stated to have relatively poor room tempeature keeping properties. But if stored at freezing temperatures it can last for years before mixing. I've stored mine in the kitchen freezer (~5F/-15C, with defrost cycles) in an opaque bag for as log as two years with no apparent ill effect. This allows for larger quantity purchases. (Of course, YMMV.)
* If someone has better knowledge, please post for those of us who do use it. Thanks.