xargs causes awk to run several times. Change "xargs awk" to "xargs cat |awk". This way xargs invokes cat as many times as needed then all the concatenated data is fed into one awk.
take a look at my previous suggestion - substitute the 'myFile' with the wild-carded file names for month of September. I we don't know how your files are named, it's hard to provide a more detailed...