What is the shelf-life of store-bought commercially-produced jam?
Jam and jelly have VERY long shelf lives both in the cupboard, unopened as well as in the refrigerator. The acidic environment and concentration of sugar make it an inhospitable environment for bacterial growth.

Typically the only changes you'll see are darkening of color (unopened in the cupboard) and possible "sugaring" in the refrigerator (development of sugar crystals).  Flavor can diminish over time too.  There's very little need to be concerned about it being safe for consumption....mainly palatability will be affected with age.