Whoa! Hang on a minute. It can only be a Korean Cort made Greco if it has no serial number. Some Grecos with no serial numbers were also Japanese and made by Tokai. There are a lot of differences between the no serial Korean Cort made Grecos and the no serial Japanese Tokai made Grecos.
The Greco above is Japanese and probably made by Fujigen. From what I can work out Fujigen made the MYYXXXX (example C843453 = March 1984) and the YXXXX (example 84565 = 1988) type serial numbers but why Fujigen was using 2 serial number formats is not really clear. On the Orville by Gibson reissues both Fujigen and Terada use 2 different serial number formats similar to the Grecos like GYMMXXX (example G304563 = April 1993 Terada), GYXXXX (example G35676 = 1993 Terada), YMMXXX (example 304563 = April 1993 Fujigen), YXXXX (example 35676 = 1993 Fujigen). G=Terada, no G = Fujigen. Y or YY = year, M or MM = month, XXX or XXXX = production number.
Notice that in all the Greco and Orville serial number formats above that one serial number format has the month info and the other serial number format doesn't have any month info. So some Greco and Orvilles have month dates and some don't. Maybe it's done that way because the guitars with no month dates were stored at Fujigen or Terada and released to the distributor (Kanda Shokai/Greco or Yamano/Orville) some months after the guitar was actually made.