Under-age (not underage as in too young) but state of being under as it relates to inventory. Synonyms include shortage, dearth, under stocked, insufficiency and scarcity. Antonyms include overage.
1. We won't make it through winter with the under-age of our supplies.
2. We thought we were going to have an overage, but it turns out we have a under-age, oh well.
3. You always have to be mindful of your under-age.