Hi there!
The first two octets are the important ones - major and minor version.
The E-Series product line has a long history of OEM usage - so we make software and hardware for others to resell, based on the E-Series platform, but with different branding. This flows on into documentation, software, user interface, hardware, etc.
Usage varies based on what part of E-Series is being discussed, but generally the third octet is based on which company it is branded for, and the 4th one is a build number.