Old Stock

I went into Checkers last month and bought a jar of Cross and Blackwell mayonnaise. When I got home and opened the jar everything was off. The mayonnaise had a very strong egg smell an was thick and stiff in consistency. I checked the expiry date and the jar is only suppose to expire in the new year.<br> <br> Was the expiry date just wrong or was the item just sitting too long on the shelf? Any explanation for this would be appreciated as I really do not enjoy wasting money on items that cannot be used.