In trying to write some reports to get VMGuest statistics out of NPM I have run into a few problems and I am wondering if anyone else has had success in getting VMGuest stats.
What I am trying to do is get the following information for the past month.
VMGuest Name
OS
Allocated Memory
AVG CPU Load / Memory Usage / Network Tx and Rx
Max CPU Load / Memory Usage / Network Tx and Rx
There appears to be data in the Database however some of the data doesn't seem to be kept historically. I am also questioning the accuracy of the roll up data 
VIM_VirtualMachineNodes has a lot of good data. The columns I am interested in are:
CpuLoad
MemoryConfigured
MemoryShares
MemUsage
MemUsageMB
NetworkTransmitRate
NetworkReceiveRate
In looking in the other views it seems like VIM_VMStatistics keeps the historical data. However the MinCPULoad, MaxCPULoad and AvgCPULoad columns are no where close to the data seen in VIM_VirtualMachineNodes. It looks like these numbers are the VMGuest machines Load % of the actual Host and not the allocated CPU to the Guest OS (VIM_VirtualMachineNodes CpuLoad matches that of the Guest OS).
Still looking at VIM_VMStatistics the Memory is definitely just the % of the Host ESX server however this number means nothing if the VM moves from a Server with say 96GB of RAM to one that has 256GB for example.
Next regarding VIM_VMStatistics is the Min / Max / Avg Network Transmit/Receive Rate columns. These seem to be way off compared to VIM_VirtualMachineNodes. The NetworkTransmitRate and NetworkReceiveRate columns in VIM_VirtualMachineNodes seems to match the actual Network Tx/Rx (in MBps and not Mbps but that I can deal with ... )
Now in the VIM_VMStatisticsByDays view, this looks to be a role up of VIM_VMStatistics however when this happens the Max numbers for CPULoad, Network etc seem to be much higher than the details in VIM_VMStatistics.
I have looked at the VIM_VMStatistic, VIM_VMStatisticsByDays Views the VMStatistic, VMStatisticsByDays Views and the actual VIM_VMStatistics_Daily/Detail/Hourly tables.
I am not a database guy so I could be all turned around on this. Any help would be greatly appreciated.