Unexplained mysterys, or maybe it's the "old math", done in a new way. I didn't catch this until the frame had been joined and splined, by my customer calling wanting the exact rabbett size. A gut wrenching moment, as we are on a deadline.
Once I've confirmed my idiocy, rather than rush into correcting, I've found it's better to walk away for a bit; let the nerves settle, and think about the proper procedure for correction.
And here, waiting for splines to be fit and glued in, and the proper size now.