I do not know this for a fact. I don't even know if there's any remote relationship. But it's an invite for others to try to figure out 'where "I" space comes from' -- how that "I" number is determined.

The reason I asked is that on Wednesday I flew ICN-YVR on AC. Originally there was no "I" space on either of the two flights that day. So in considering my options I had to decide between flying AC or SQ in paid J, or maybe even flying CX in paid J, which would definitely lock in my BA Gold status when I compete some already booked flights later in the year. But in the meantime, an I1 suddenly appeared on the early flight, so I booked a Y fare and requested (and was granted) an upgrade. (The later flight continued to show I0.)

The strange thing was that the seat maps for both flights showed the J cabins to be virutally empty, and in both cases the flights showed J9 and fairly high (i.e. 6-8) for C. Now as we all now, the seat maps are not necessarily and accurate representation of J availability.

But once I got on the plane and saw only 6 people in the J cabin (out of 24 seats) it became prefectly clear that in this case, on at least this flight (and I'm guessing also on the second flight) the J cabins really were all but empty. (I had to chuckle when the FA apologized for "rushing the meal service", though unintentionally. Seems there were so few J passengers, she was running out of things to do. But I liked the service just fine.)

But back to the fare class availability numbers... after I made my booking, the I number changed back to I0, and then sometime later back to I1. Meanwhile the later flight always showed I0. And the only difference I could discern was that my flight also showed L2, while the later I0 flight showed L0.

Now were only talking about a sample size of 1, which ain't really a sample size at all. But it did get me wondering if upgrade space has recently become more a function of Y space and less of J space. I still trying to figure out if there's some possible logic to such a scheme, but jet lag still has my brain in a gellified state.

Any other thoughts?