I found this info on the American Pernicious Anemia site.
perniciousanemia.org/b12/in...
Does Injectable Vitamin B12 Go Bad Or Expire?Does injectable B12 ever expire or go bad?Obviously yes, but it’s often way past the expiration date stamped on it:Properly stored vitamins are likely safe past their expiration date for up to two years. Water-soluble vitamins, such as B12 and C, are more likely to lose their potency quickly. Expired vitamins will not become poisonous, but rather lose their potency. Exceptions to this rule are if supplements are stored in wet, hot, or humid areas and produce mold. Moldy vitamins should not be consumed.SHANNA LEVINE, MD, MOUNT SINAI HOSPITALThe expiration date on meds is the time limit that the dosage potency is guaranteed. After that time, the potency may be less (but often is not). It is the rare drug (some types of tetracycline) that become toxic if outdated. Nevertheless, a pharmacy can not dispense, and a physician is not supposed to administer a medicine beyond its expiration date.