Welcome to the Community.
WD constantly updates drive revisions as soon as manufacturing or firmware improvements are deployed. However, revision details are not available to the public.
Maybe you should try contacting WD’s Technical Support about this. You can do so either by phone or email.
To Contact WD for Technical Support
http://support.wdc.com/contact/index.asp?lang=en
Support by Country
http://support.wdc.com/country/index.asp
