Thank you for your inquiry. We will guarantee the antibody for a total of one year. So, if the antibody was purchased 8 months ago and just reconstituted now, we will guarantee it for another 4 months.
From our general product info:
R&D Systems has established a policy of not limiting the useful life of a product by providing an expiration date or manufacture date for our protein and antibody products. Under proper storage conditions, proteins and antibodies tend to be stable for many years. These conditions include storing proteins as lyophilized powder, storing the product frozen (-20° C or -80° C) at protein concentrations of greater than 0.1 mg/mL, and limiting the number of freeze/thaw cycles. Please see individual product datasheets for specific instructions. Routine quality control testing by our company ensures that all products have acceptable biological activities at the time of sale. R&D Systems cannot control storage conditions of a product upon receipt by the end user. In lieu of an expiration date, we choose to offer a warranty on our protein and antibody products. All products supplied by R&D Systems are warranted to meet or exceed our published specification when used under normal conditions in your laboratory. Typically, this warranty will extend 6-12 months from time of purchase. Please see individual datasheets for specific stability claims. If the product fails during the stated period, a replacement product or credit will be issued. For details regarding our warranty please see http://www.rndsystems.com/customer_service_legal.aspx.