In many cases, there is confusion between Expiry Date and Retest Date and expiry being used instead of retest.

As per ICH Q7, 

Expiry Date: The date placed on the container/labels of an API designating the time during which the API is expected to remain within established shelf-life specifications if stored under defined conditions, and after which it should not be used.

Retest Date: The date when a material should be re-examined to ensure that it is still suitable for use.

ICH Q&A in Section 14.2, clarified this point:

According to the definition, the material should not be used after the expiry date. The original intent of this definition in ICH Q7 was that expired API should not be used in drug product formulation.

Expiry Date means there is a known quality attribute that is at risk beyond the time frame supported by stability data whereas retest indicates no known quality risk. If API COA gives a retest date then it can be used after retesting with support of appropriate stability data. If the COA gives an expiry date then API should not be used in drug product formulations after its expiry date.