The "close" price is determined at 4:05pm, just after the closing price auction. Any aftermarket trades after this time do not affect the day's price.
The day's volume is affected by aftermarket trades and this is probably where you're seeing different volumes.
The ASX do not official "close" their equities systems until around 7pm EST, so you will never get the final volume figure before this time.
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Have a look around at the different data vendors - trial their products and make your own assessment.
