Let me get this straight. There are three options:
1. An artist who has always been a little loose with some details forgets a detail that wasn't important except to prevent a plot problem one year ago, after a particularly bad injury (for a professional artist) and receiving the most money he's ever received in his life, or
2. A group that has used several hours to prepare for this encounter spends part of that time actually preparing for this encounter, or
3. The most consistent honest and dutiful character the strip has seen told a useless lie just to avoid doing his duty when the fate of the world depends on success.
And you think the most likely theory is the third one?
I ... disagree.