Yes, I agree--I'm picking them early on account of the birds, but also because they ripen so fast, I'm afraid I'll not be able to get to them before they really ripen and maybe drop. I can only take it on faith this is indeed a ZDSC, as that's what the tag said. On this one I can see the graft.
On the other tree I got at the same time I can't see a graft line. Last year I got dark fruit off it. So far I've not seen dark fruit, but it's a bushier plant more amenable to birds.
Here's a pic of a fruit from last year showing how dark these fruits got.
I have to say, these have gone from just another fruit tree to have in the yard to something I'm really enjoying.