signature "in the stone is a pat of the print. The signature on the MAT seems weird as its not the normal way of signing a real print approved or pulled by the artist. Are you sure Ching signed the mat?
Im not fmilir with this artist but maybe if you contct him or hi agent and find out why it was signed in the mat instead of on the paper. We often change mat of works since mats can get dirty nd are often chosen to "go with the wall" . If his sig is real, you seem to be stuck with that mat.
I don't know what to say other than that.