After a certain size of servers, it is impossible to remember whether they are all current or not, or even check a documentation wiki page to find out about. So how can one use ansible to find out the answer? The setup module enters the room. Assuming an all Debian installation one could run:
ansible debian-machines -m setup --tree /tmp/invetory cd /tmp/inventory grep ansible_distribution_version * | grep -v 7\.2
This will list Debian machines not running 7.2 (Wheezy). You can build more complex versions of the above to match your infrastructure.
PS: Many thanks to @laserllama and @jpmens.
Managing organized complexity 