Analyzing the same files in different SDL Trados versions

I have been facing problems with different translation analysis results. To be more detailed - I use SDL Trados 2011, 2014 and 2015 and there have been cases noticed when different versions show completely different word counts for the same files analyzed with the same translation memories. For example, SDL Trados 2011 shows 4000 words but at the same time SDL Trados 2015 shows 5000 new words for the same file. I know there might be some small differences in numbers but there are cases when the difference is one quarter from the whole word count which is does not work at all. Maybe there are some settings I need to adapt, could you please suggest on this issue?