It should be 6 digits + 2 letters, the letters representing the country code, e.g. JP for japan, KR for korea etc. Never heard of a country code 5K, to be honest. The serial number (7 digits on shaft, above production code) is hard to read, is it painted on ? Serial number and production code are laser engraved on original rackets, so they can't be rubbed off.
JP uses the symbol that is at the end now. By the image provided, this would have to be a JP racquet if it is legit Sent from my Pixel 7 using Tapatalk
When the old setup of the number is still valid, the production date would be 07.06.2008 or 07.06.2018 or 07.06.2028. As far as I know the 100zz has a release date of late 2019/early 2020.