I've had five fruit from my Amethyst drop--all Caerulea pollinated--and they've averaged 8-10 seeds in each fruit. The sparse fruit pulp isn't very pleasant for any of you out there that may be curious.
My Lady Margaret has three fruit that seem to be maturing happily--two caerulea pollinated and one Constance Eliott. My attempts with incarnata haven't taken. The fruit are interesting, in that they have darker green longitudinal lines running down them. Hopefully, there will be some viable seeds inside them.
And after years fruitless (ha) pollinations efforts on my part, my Incense has three fat fruit on it--two caerulea and one incarnata. It's willingness to fruit this year leads me to think that yes, plant maturity is a very big factor in getting Incense to hybridize. Will let everyone know when the fruit drop, and if they have any seed.