How does AOAC interpret sample weight approval?

AOAC PTM Validations list weights next to matrix type, what does that mean?

If you search approved methods on AOACs Certified Method Website, the description of the method will list matrix type and weight.  See the example below:

The listed weights indicate the method is approved for UP TO the weight listed.  This does not mean you must test the weight listed.  In other words,  AOAC does allow certification of smaller test portions using the same dilution ratio as the validated test portion. 

For further reference please see the AOAC Technical Bulletin on the topic.