The daily short volume number is mostly not meaningful. The reason is that if a MM sells to a customer short that number is reported. If the MM buys those shares back on the next trade he is now even but the short vol doesn't change. That is just one example of how that short number is generated.
If you look at the daily short number for a stock over time you will see that it averages around 30%.
Now think about that for a minute, is it possible for 30% of the volume to be short everyday? Obviously there has to has to be a lot of short covering every day or the entire float would soon be short and the monthly short interest data says that is not true.
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