When installing the 2014.3.1 update, depending on how it is installed, there are different versions shown by Vivado:
2014.3.1 updated via Xilinx Information Center (XIC) or manual update from the download page:
2014.3.1 installed with a full installer:
These build numbers are intentionally different.
The individual update file only delivers 17 files from the new build and does not affect the other files that came from the original build.
For that reason the build number is not changed, even though it is a hybrid of the two builds.
When installing the full image of 2014.3.1 however, all of the files are from the new build, which shows the different build number.
The two installations contain the same content.