Identifying dependency between CRM ABAP and CRM JAVA

Hello Experts,

We have CRM 7 dual stack installation. ABAP and Java stack both are on SPS6. Now because of some prerequsite I need to upgrade CRM Java stack to SPS9. I just want to know is it mandatory to upgrade even CRM ABAP stack to same level ?

Is there is any SAP note which talk about this dependency (I am not able to find).

Regards,

Abhijeet