Makers like ARF, NOOB and ZZF are making excellent watches and flaws determine the difference between good and a great.
Regarding the serial numbers, the XX could Identify a watch as a ZZF. Its also possible a Gen serial number beginning with X could exist however, I've never seen one so can't say. Thus considering ZZFs all start with X it's a safe assumption that a person with knowledge could immediately recognize a ZZF.
The point I was trying to convey is the rehaut and the subsequent numbers are so small it's not possible to see without a macro picture or magnification. Therefore, not likely a flaw someone would call out.