PIOMAS is an ice volume model - whose numbers are derived from multiple sources of data, not any particular "sensor" - and the far superior one, by any scientific standard.
But hardly hard factual data recovered from tens of thousands of data points delivered by tens of thousands of monitoring systems. It is, as you say, a model of these "available" data which are hardly complete. Meaning that PIOMAS has to fill in the blanks.
PIOMAS is an excellent tool which is, as you say, the best of the available tools we can use.
That being said, it is a Model and is not hard data. In a time of extreme change, where the modelling is behind reality, then it is likely to have significant challenges in terms of correctness. The problem with the Arctic and forecasting is that it is vital that certain areas are absolutely correct in order to try and forecast the impact of any weather events. PIOMAS can supply overall certainty to a high degree, indeed the highest degree currently available, but it cannot tell us, with a high degree of certainty, what is going on in some of those vital areas.
This has been seen and proven over and over again and it does not do PIOMAS the credit it deserves by insisting that this is not the state of affairs.
I would strongly recommend you to adjust your personal perceptions so that they fit certifiably accurate data
Re: the statement above I would change that to
"Certifiably MODELLED data"
Besides, there is nothing particularly extreme about this melting season, and this seems perfectly reasonable to assume that volume and extent/area measures would realign again as minimum approaches.
Personally I had thought that 2007 and 2012 were outlying years of such spectacular change to make them "Extreme" in every sense of the word.
2017 extent, today, sits < 50kkm^2 above 2007 and below all other years. At a time when 2017 is showing massive potential for ice destruction from the most moderate storms, smack in the middle of the post 2012 "storm season".
In the next 5 days, 2012 parted company with 2007 and headed for a new record. 2017 is showing signs that it could go either way, 2012 or 2007. But it has firmly crashed through 2011 with no sign of slowing. If anything, the opposite.
It is so comforting to know that 2007 and 2012 are now considered so unexceptional that a year which is tracking them could be considered "normal".
Whilst there is still opportunity for 2017 to stall and fail to make a new record or, even, to finish between 2007 and 2012, there is also ample opportunity for 2017 to crash through 2012 and head for the record books.
The most extreme thing about 2017 was the winter/spring warmth. All things being equal, that extreme weather is unlikely to have no impact on the summer low. Given the summer melting season we have had, 2017 should already be heading for a 2010/2011 track. The fact that it is not should be warning enough of the potential to come.
Whilst none of us are experts in this field and all of us welcome being corrected in our assumptions, it is best if the correction is entirely accurate and not the aspiration of the person who is correcting.