Hi Joshua,
I do the primary forging at around 2000 °F and don't go lower than that till the finish. I think that you may be right, because the one that didn't delaminate I kept at high heat, few strikes and back to the forge. I've read in some older posts that there is benefit in cold forging and that the nickel layer helps to keep everything together. I water quenched one of the blades that had minor delamination and it didn't open up, that is another thing that I've read in older posts, that fast quench is better for san mai. I've got some billet left, one with mild steel