DISCUSS EP5.10 control of impurities in substances for pharmaceutical use

In the subparagraph" interpretation of the test for related substances in the monographs on active substances" there is a sentence:

“where a general acceptance criterion for impurities equivalent to a nominal content greater than the applicable identification threshold is prescribed, this is valid only for specified impurities mentioned in the impurities section.”

According to the definition of “specified impurity” therein, query, how can a “specified impurity” be related to “general acceptance criterion”?