Thank you. You are undoubtedly right about the spinnaker. Not so sure that this is a brochure photo since I've seen no evidence that Pearson ever offered an inner forestay of any sort on the 10M. Probably will never know for sure. In any case, I'll get with my rigger. EAP
It's not an inner forestay. just a free flying jib attached to the jib halyard with the tack attached to something on deck aft of the normal jib tack position. I seriously doubt you ever want to have a inner stay from which you would hoist another sail. on this particular bout. The foretriangle looks too tall and skinny.
A 'baby stay', maybe which would have an entirely different function.