Ubuntu – Does an older kernel source get installed

I am running Ubuntu 14.04 kernel 3.19.0-39-generic and wonder why when installing the kernel sources version 3.13.0 of the kernel source actually gets installed..?!

~# uname -r
3.19.0-39-generic

~# apt-cache search linux-source
linux-source - Linux kernel source with Ubuntu patches
linux-source-3.13.0 - Linux kernel source for version 3.13.0 with Ubuntu patches

~# apt-get install linux-source

..(would install linux-source-3.13.0)..

After installation:

~# ll /usr/src/
total 28
drwxr-xr-x  7 root root 4096 Dec 10 15:12 ./
drwxr-xr-x 10 root root 4096 Aug  5 01:12 ../
drwxr-xr-x 24 root root 4096 Dec  4 12:13 linux-headers-3.19.0-37/
drwxr-xr-x  7 root root 4096 Dec  4 12:13 linux-headers-3.19.0-37-generic/
drwxr-xr-x 24 root root 4096 Dec  7 09:45 linux-headers-3.19.0-39/
drwxr-xr-x  7 root root 4096 Dec  7 09:45 linux-headers-3.19.0-39-generic/
drwxr-xr-x  4 root root 4096 Dec 10 14:55 linux-source-3.13.0/
lrwxrwxrwx  1 root root   47 Nov 30 23:38 linux-source-3.13.0.tar.bz2 -> linux-source-3.13.0/linux-source-3.13.0.tar.bz2

I am digging into this because I am having notorious problems installing the NVIDIA kernel driver modules and the installation fails with unable to locate kernel source. (I know it's only the header files that are needed, but I am out of options and look in all directions..)

Thanks