What does 'w/31 bit PCCA' mean?

Beginning with z/OS 1.9, IBM introduced a new SYS1.PARMLIB(DIAGxx) parameter to move some control blocks (accessed by our products) to 31 bit storage:  

 CBLOC VIRTUAL31(IHALCCA,IHAPCCA)

IBM ships z/OS 1.9 WITHOUT this parameter coded. 

If you INCLUDE this parameter, you MUST run the minimum release (or higher) identified in the last column of the Product Release Table.

If you do NOT include this parameter, you MAY run the release identified in the last column of the Product Release Table, but MUST run the minimum release (or higher) identified under the z/OS 1.9 column.