What is the code in the gulp-concat plugin?

Question

Node.js

Learning to write plugins for gulp. At first I decided to study the code of the most popular ones.
Two points in the gulp-concat plugin code are not clear :
1. Why do we need to manipulate the latestFile and latestMod variables? After all, endStream is so executed only 1 time at the output. Why choose the most recent file and modify it?
2. The question follows from the first. Why is the latest incoming file cloned here instead ofvar joinedFile = new File(...)