I am not with Biotest but I can “kinda” answer this question, having worked for a company that makes supplements used by many other companies.
THe goverment requires labeling best use by/expiration dates of food/food related products to provide a baseline period in which the quality of the product is supposed to be 100% or as close to it as possible.
That does not mean that this is the real expiration period. Many times the date is set for a shorter period than necessray as a conservative estimate of how long the item will remain “good”. Other times, the shortened date is set to ensure quicker turnover of product (and get the customer to buy more).
The reality is most supplements (vitamins/minerals/sports nutrition) have a lot longer “real” date that what is on the container. Yes, some products do go “bad” quicker (the closer to natural that it is, the amount of fats/oils in it, et al). But the reality is, there is likely to be little or no degredation of the product or its efficacy within a reasonable period after the expiration.
Short answer, your creatine is just fine.