Hello,
The "shelf life" is likely to depend on whether the device is already mounted to the circuit board, or not, and the conditions under which the storage takes place.
If the storage takes place prior to being mounted, maintaining solderability of the pins is likely to be the main issue. Storage in a damp "tropical" climate is likely to be a problem, especially if fungal growth can occur.
It is possible for the device package to absorb moisture over time. With SM devices, this can give reliability problems during the reflow soldering process, unless baked for a lengthy period prior to use.
These considerations would dictate that, for long term storage, sealed packing should be used, that incorporates a desiccant.
Regards,
Mac