ArmorCore has no expiration date.  As long as it is not exposed directly to U/V rays, chemicals, etc. it should not break down. When used in construction projects, they say it should last the life of the building.
As a Level 3a+ plate it should again last a lifetime. 
One suggestion is to paint for easier handling & to extend the life.  
DON'T RUB HANDS ON PLATE UNTIL YOU SPRAY PAINT! BETTER THAN STEEL: -LESS WEIGHT-NO SPALL BETTER THAN KEVLAR/ARAMID/PE: -STAB PROOF-LAST LONGER-ABSORBS MORE OF THE IMPACT
Included in this listing: Vest
CORDURA® construction with reinforced stitching
MOLLE: integrated modular webbing on front and rear of vest for easy gear customization/mounting
Accepts up to 10 1/4" X 13 1/4" front/back plates and up to 6" X 8" side plates
Adjustable/removable cummerbund with pockets for side armor
Quick release side plastic buckles
SIZE: Adjustable Medium - XXLPlates
4) High Quality FLAT ArmorCore Plates (10x12 & 6x8) Rated Level IIIA+
Tested with multiple rounds including .44 Mag @ 10 yards (Zero Penetration)
Plate edges are smooth and free from burrs or sharp edges
The plates are cut for an ambidextrous comfortable fit
Each 10x12 plate weighs 3lbs 14oz and is a 1/2 inch thick (HALF THE WEIGHT OF STEEL)
Each 6x8 plate weighs 1 lb 11oz and is a 1/2 inch thick** This model complies with NIJ Standard-0101.06 for Ballistic Resistance of Body Armor **15% restocking on all returns
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Legal Notice
It is important to remember that nothing is "bulletproof" and that there are many variables at play which allow any type of armor to stop a given object. There will always be danger in these types of situations.
We will only sell armor to law-abiding adults who have no felony convictions, and are not involved with criminal organizations.Residents of Connecticut are prohibited from buying Body Armor. We will only ship to states where Body Armor is allowed, please know your local and federal laws prior to purchasing. By purchasing, you agree to this and all terms listed on this page, and Body Armor Megastore
By purchasing you assume all risks of use or misuse, and agree not to hold us liable in any way. In addition, YOU are responsible to ensure that your ballistic panels are properly inserted and installed.
Body Armor Megastore and any of its affiliates assume NO liability.
We neither assume, nor authorize any person to assume for us any liability in connection with the sale or use of the goods sold, and there are no oral agreements or warranties collateral to or affecting this agreement. We hereby give notice that any statement made by us in the sale of the goods, shall not create any warranty that the goods shall be fit for any particular purpose. Statements, images or descriptions are informational only, and not made or given as a warranty of the goods in any way. We specifically disavow any other representation, warranty, or liability related to the condition or use of the goods.
We do not cover any consequential damages, and our liability is limited to repairing or replacing defective goods. This product is sold "AS IS" and "WITH ALL FAULTS". The entire risk as to the quality and performance of the product is with the buyer. We are not an insurer, and bear no liability for any use, misuse, or failure to perform. All warranties including the implied warranties of fitness and merchantability. Incidental and/or consequential damages are excluded. Purchaser covenants and agrees that the purchaser or his/her heirs, agents, assigns shall NEVER bring any action in any court of law from any dispute arising from the Purchase and Sale of product(s) sold by Body Armor Megastore or any of its affiliates. If any part of these terms is held to be invalid by a court of competent jurisdiction, such shall not affect the validity of any other part of these terms.  Headings are for convenience only, and do not limit or affect these Terms. These terms may be updated without prior notice.
In accordance with Marketplace Fairness Act & Remote Transactions Parity Act  ALL Customers are liable for all Federal, State and Local Taxes due.  We will collect and handle sales tax for customers from our home state of PA.
CONSUMERS SHOULD SUPPORT - H.R. 6824