Reject PCB's on Panel

[JivenJim]

My MFR has asked me to spec out the number of acceptable PCB's that are marked with a black inked X on a panel (thus denoting that this PCB is not to be used) I looked though IPC-600 but found no standard or mention of the infamous black X. Calling out a straight % of acceptable bad marked PCB's/panel could vary greatly. 1 out of 3 would be 33% bad; and would be acceptable to me. But 33 out of 100 would be ridiculous. Anyone have any suggestion or know of a governing spec. I also heard 10% failed, is an industry guideline but haven't seen it written.

Thanks

Jim