I suspect the reason that their drilling only one Mereenie well...

I suspect the reason that their drilling only one Mereenie well isn't forecast to affect the reserves upgrade is because the Mereenie drilling is not about finding more gas (which is already known to be there in the Stairway) but proving that horizontal wells can commercially produce the 2C resource where the existing verticals couldn't.

It's a technology trial. The reservoir characteristics are fairly well understood so if the trial is successful the certifier can apply the results to the field model and upgrade the 2C to 2P where appropriate.

Obviously two wells are better than one for this as they provide more confidence, but one well is sufficient if it's successful.