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What is the difference between FINRA share volume and NASDAQ share volume?
Assuming the data you're referring to is this line: the difference might be related to the different exchanges on which the stock trades.  FINRA could be listing the reported volume from one exchange, while the NASDAQ data might be listing the volume on all exchanges. This is an important distinction because AAV is a Canadian company that is listed on the Toronto Stock Exchange and the NYSE. The Q at the end of the line stands for NASDAQ, according to FINRA's codebook for those data. My guess is that the FINRA data is only reporting the volume for the NASDAQ exchange and not the total volume for all exchanges (Toronto, NASDAQ, NYSE, etc.) while the data straight from NASDAQ, oddly enough, is reporting the total volume. However, FINRA could also face reporting discrepancies, since it's a regulatory body and therefore might not have the most up-to-date volume data that the various exchanges can access.  I don't know if it's related or not, but looking at the NASDAQ historical data, it looks like the volume on March 6, the day you're asking about, was much lower than the volume in most of the days immediately before or after it. For all I know, something might have happened that day concerning that particular stock or the market as a whole. I don't remember anything in particular, but you never know.