OK all, got some answers from FINRA about the daily aggregate short numbers. Turns out my interpretation is right but there's a big caveat that essentially makes what some others were saying actually truer in a practical sense.
So if you have a total volume day of 10,000 shares and 5,000 shares of those were reported in the aggregate short, what this should mean is that at most 50% of the total volume was shorted and still open at the end of the day (to make market most likely, but *can* include retail shorting), and at the least 0% is still open as for each reported short there was enough total volume to have a cover cancel it out. This cover would/should be reported in the daily total volume. So 1 share is shorted it shows as 1 share in short volume *and* 1 share added in total volume, then when that share is covered it is again added to the total volume since it was another transaction but not taken off of the short volume count. So in theory, the daily REG SHO numbers can give us upper and lower bounds on what is possibly still open shorts at the end of the day. Track it long enough and I imagine you could get a trend and glean some useful info.
However, here's the big caveat. The numbers are "media reported" (FINRA guy's term) and are not guaranteed to be correct because a single share can be stepped on so many times during a day and often only one of those times is it actually reported as a transaction. So if the MM's want to hide transactions they can do it very easily and it would screw the above theory up pretty royally.
According to the guy I talked to at FINRA, the daily numbers are just provided as "another data point" and though he said the above theory is how it is supposed to work, they can't guarantee that is how it is working on a day to day basis.
Thanks to those that prompted me to look further.
BOOM!
