Did I forget about some web server in my dmz (?)

Ok so you’ve been working like h#%”# for a couple months (mabye a year), implementing new application servers, moving around services, upgrading other servers and pretty much been busy. Of course you’re updating documentation all the way ! :p … But for that 1 in a million incident where you just happened to forget about updating the documentation of your servers, say you wonder about “do I have control of all my web servers now ? is it possible I might have forgotten to stop Apache on some random server (?)
nmap comes to the rescue, say I want to find every server in the subnet listening to port 80:

nmap -p 80