Looks wide open to me.
The maximum number of seats shown is 7 in Economy and 4 in PE or Upper (depending on the GDS you're using). Therefore, J4 means at least 4 seats available in Upper, and Y7 means at least 7 seats available in Economy.
Also, each bucket is a subset of the most expensive (full fare) bucket in that cabin. In Upper, for instance, Z is a subset of D is a subset of J. To try and make this clearer, let's say you were looking at a readout such as J4 D3 Z1. You don't add the numbers together to get the total availability, in this case it would mean there are at least 4 seats available in Upper, 4 or more of which can be had at full fare; 3 of which can be had at the D bucket price and 1 available in the Z bucket. The cheaper buckets tend to go first, but there is nothing to stop someone paying for a more expensive bucket if they want more flexibility, better mileage, or whatever there reasons. If someone were to by the 3 seats in the D bucket in the above example, the readout of Upper is likely to change to J? D0 Z0 (I'll come back to that ? in a moment...) because the 3 seats that could be bought in D included the Z buckets too. Hope this is making some kind of sense.
Right, back to that ? in the J bucket. When someone bought those 3 seats in D, it would have reduced the total availability of seats in the J bucket too, but because J was at J4, you don't have any sure way of knowing how much supply is behind that at full fare.
Also, note that reservations are being changed and/or cancelled every minute, so looking at the availability only give you an indication of how busy the flight is at that moment. It also important to realise that this is 'availability', not 'physical seats'. You probably already realise that every airline oversell their seats because of no-shows and last minute cancellations. In fact they have a complex set of calculations that help them predict just how many people will not appear for a particular flight. They then oversell seats based on this calculation, and the availability is showing you what you can buy; not how many seats are left. A subtle difference, but worth remembering.
Because cheaper buckets sell out first, watching the availability from the right hand side is a good indication of whether the flight is busy. In your examples, there's M7 (maxed out) on all of them - so absolutely wide open.
However, this is for a flight in January next year - so way too early to predict whether the flight will be full. Good time to be picking up the bargain buckets though...
Hope that made some sense!
Pix
