What is the difference between glibc-2.12-1.166.el6_7.7.i686.rpm and glibc-2.12-1.166.el6_7.3.i686.rpm

I've always believed that with a package name like glibc-2.12-1.166.el6_7.7.i686.rpm, the glibc version was 2.12, the RH version of that library was 1.66 and el6_7 referred to the OS version number. What is the significance of the .3 or .7 after the version number?

As you can see from my example, I am trying to decide if I need to patch my O/S, again. I patched in January and glibc is glibc-2.12-1.166.el6_7.3.i686.rpm. The RHEL notification for CVE-2015-7547 points to glibc-2.12-1.166.el6_7.7.i686.rpm.

Any ideas?

Cheers!

Robert