I considered using the possessive at 10d but opted for the alt sp for the definition at 7d instead - this gives a 10th three letter curtailment (but can either be said to be definitive?).
The wordplay in 7d leads to an entry in Chambers which is a specific choice of spelling options for the definition. But that's just my understanding of what I see.
OK never mind I was just trying to help. I'll just go back to passively watching the thread. Every time I try to be an active participant it gets confrontational! Ho hum.