How do I know what linux kernel version does a distribution use?

When I run

uname -r

I get 3.2.0-4-686-pae on my Debian7 and 4.4.26-gentoo on my Gentoo.

But what I can't find anywhere is what Linux kernel source versions do these distributions use. If I understand right all distributions take the kernel source code from here https://www.kernel.org. So how can I find out what Linux kernel versions from the site do use 4.4.26-gentoo or 3.2.0-4-686-pae, for example?