There are a few possibilities here:
1) If a system hasn't been online or connected to ePO in the last 3 days, it will report in ePO as having an older version of the DAT (even if it has upgraded).
2) Some of those systems are configured to use a distributed repository that isn't updating from the master repository. Given the size of your environment, I'm guessing that this is not the case.
3) Some systems aren't updating. This can be caused by a broken Agent or a broken VSE installation. Your "1111" DAT systems are likely in this bucket, or they were just recently built and haven't updated yet.