What is the shelf-life of store-bought commercially-produced jam? My question is similar to this one, but about store-bought jam.

What is the shelf-life of store-bought jam &ndash; i.e. commercially prepared major brands &ndash; if not opened?

Are the processes or ingredients for preservation of mass-produced jam superior to at-home sterilization of home-made jam?

Quite simply: I have an unopened jar of jam purchased 18 months ago.  Good to eat now, or not?
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.