Getting our systems software inventory into compliance

I have about four hundred computers that I am responsible for in terms of both the hardware itself and the software that runs on each system. As unwise a practice as it may sound, we have not been all that diligent with keeping track of out software inventory over the years. We keep pretty good track of the operating systems because we know they are associated with the machine itself and the license label on it. As far as all the secondary applications installed on each machine, those are the ones that we have fallen behind on in keeping track of software inventory. Which is kind of a problem for me and my team right now as we are on a big push from corporate to get our software inventory up to speed and have it be fully compliant. That means that every bit of software inventory we have has to match our owned licenses on a one to one ratio, no exceptions allowed. This is to mitigate the risk of being caught out of compliance as the result of an upcoming audit. I can say with almost complete certainty that our software inventory does not match up with the licenses we own. Either we do not own enough, or the ones we do own are not the correct version. I know that we might not be able to afford to buy enough licenses for everyone to get the software inventory up to snuff, which means bad news for a lot of people. The software inventory will have to be assessed based on individual need and priority. If a program is not absolutely needed to do a job, then the program will have to be uninstalled from the computer. I hate to do it to people, but we are under strict orders to get our software inventory under control and we have no choice.