That is good to hear- I just grafted a bunch of Kokuso onto a wild mulberry growing by the road. I also added a few Oscars. I also tossed a Kokuso onto the Gerardi.
I’m not sure how well I’ll do on these grafts- the only mulberry grafting I’ve done was 1/3 last year, with Illinois Everbearing onto the same wild bush/tree.
Here’s what the graft looks like after a year- I’ve circled both the IE leaves (almost circular) and the rootstock (multiple lobes). Both the rootstock and the IE have fruit, thought he RS’s fruit is much smaller.
The kokuso looks a lot like IE and both have big leaves (possibly due to Red mulberry heritage?). The Oscar is somewhere between the IE and the rootstock in terms of leaf shape and has smaller leaves (100% white mulberry?).
Here is a good page for distinguishing Red vs White mulberries.