All films change over time, losing contrast and color balance. This is a gradual chemical reaction, the rate of which is a function primarily of storage conditions.

High storage temperatures accelerate change; low temperatures slow it; freezing stops it.

Humidity accelerates it; dry storage helps minimize it.

The factory "process before" date for film is always conservative, and properly stored films give excellent images long after they have "expired." They can continue to give excellent images for many years, if sealed in moisture-proof containers (for example, Tupperware, or zip-lock type bags) and stored in your refrigerator. Freezing is even better, extending the life of your films for many decades.
Some refrigerators get rid of frost buildup automatically by periodically warming the freezer compartment. Film stored in this kind of "frost-free" freezer compartment may not last as long as it would if stored in constant sub-freezing temperature.