I haven't been following this issue closely (or indeed this...

I haven't been following this issue closely (or indeed this forum much at all), but having looked it up it's pretty clear that the missing gas is dependent on the lateral upgrade as you said in your original post.

When they announced the IPL GSA they said they were in discussions with APA about upgrading the lateral and that it could underpin Stage 2 of the GSA. But I suspect the reason why Stage 2 was contingent is that it was dependent on both the lateral upgrade and in WM26 adding Stairway reserves to justify the upgrade. Now that the latter hasn't happened, there's not much point in the former - certainly not before the NGP goes live.

Stage 2 is included in the first slide you posted but excluded in the second slide, which was post-WM26 failure. Stage 2 is clearly not going to happen this year (at least not from Mereenie) so it's been removed from the forecast. The 20 TJ/d in Stage 1 of the GSA in the first slide corresponds exactly to the 7.3 PJ/a in the IPL GSA in the second slide. The remaining 10 TJ/d is missing. Two big things happened between the first and second slides you posted to explain the apparent downgrade - the GSA went from being still under negotiation to being locked in, and WM26 failed.

That's the missing gas - no great mystery or conspiracy behind it!