Thanks for the addition info!
So my grafts to the ponderosa lemon all rotted, they turned yellowed and black. I think my grow tent is too cold, but I also suspect the scions were already too far gone. I did a t-bud, and cleft graft, and a "z" graft. They all turned yellow and then black.
Curiously the greenest cuttings I took from the top of the citron and stuck in coco-coir are pushing growth and have no signs of yellowing or turning black so hopefully they are rooting. I don't want to disturb them to check for a callus so will wait patiently for roots to appear through the bottom of the container.