On Saturday, 17 September 2016 10:42:41 UTC+1, JohnD wrote:
Isn't the explanation there in black and white on the NSIDC site, ie:

'NSIDC produces the daily extent image and graph using a five-day trailing
mean. Please note, the values provided are the individual daily values, not
the five-day average values that NSIDC displays for its daily extent image
and graph'

All you have to do is to click the 'About the data' link.

Thanks John that explains the difference between the news articles and the raw daily values!

And using a trailing mean rather than a centred mean would explain why it occurred 3 days later. But why use a five day moving average to ascertain when the minimum extent has been reached when you have daily values?

I am fairly certain this change to using a five day moving average has come in quite recently, perhaps since they started using v2 in June.