As you are finding out, every tree is unique. I don't care if you are dealing with 10 clones that are all cuttings from the exact same tree; they will all be different in one way or another.
I am curious about his shimpaku because it is turning yellow. If the foliage were dying it would normally turn brown. Where did you obtain it? I am assuming you obtained it from a different source, or at a different time, than your other trees? I have several variegate shimpakus that look similar (but different) from this... but they don't suddenly turn yellow - they have been yellow all along.