Hola Carmen!
Por lo que pude averiguar "overage" es un exceso, un agregado, un sobrante.
Para que entiendas mejor, el siguiente texto fue extraído de este link:
http://www.thyroid-info.com/articles...idproblems.htm ( Punto II)
"An overage is the amount of active ingredient above 100% of the product's labeled potency at the time the finished product is tested for release. Such an overage is intended to compensate for potential loss of active ingredient by degradation while the product is stored and thus permits an extended shelf life for a product with a poor stability profile."
Hope it helps!