That dosen't make t hem 300 man
and I dought that Office have more keys then windows , at least not that much keys (300)
1 invite gets 5 keys of each version of windows 8 and 8.1, keys which you get is windows 8, 8.1 and 8.1 with update, there 4 versions of each of them.
So, total keys for 1 invite is 12 x 5 = 60
one admin has 5 invite(including admin account) so, 60 x 5 = 300keys of windows 8, 8.1 and 8.1 with update.
Now, let's count windows 7 keys
You get total of 15 versions of windows 7 in ONE invite, each version has got 2 keys
So 15 x 2 = 30 keys for ONE invite, Admin = 5 invites = 5 x 30 = 150 windows 7 keys per admin
Now, let's count windows xp and vista keys
You get total 15 versions of windows xp and vista in one invite, each version has 2 keys
So 15 x 2 = 30 keys for one invite, admin = 5 invites = 5 x 30 = 150 keys of XP and vista
Total, windows keys you get is 300(windows 8,8.1,8.1 with update)+150(windows 7)+150(windows xp and vista) = 600 windows keys per admin
Now, let's move on to office keys
Office 2007 = 2 version each 2 keys = 2x2 = 4= per admin = 4 x 5 = 20 keys
Office 2010 = 2 version each 2 keys = 2x2 = 4= per admin = 4 x 5 = 20 keys
Office 2013 pro plus = 1 verison 2 keys = 1x2 = 2 =per admin = 2x5 = 10 keys
Office 2010 for mac = 1 verison 2 keys = 1x2 = 2 =per admin = 2x5 = 10 keys
Total keys of ms office is 60 keys.
So total of windows and office in one admin is 600 + 60 = 660
And also if there are many other software as visual studio and many others, so you will easily get more than 1000+ keys from one admin.