I couldn't say if the Latakia is Syrian or not. While I've had several Syrian Latakia blends, most have enough other components that it's hard for me to learn how to distinguish it's particular flavor. I have sometimes found Syrian Latakia to taste almost metallic in blends like Drucquer Royal Ransom and Balkan Sobranie 759, but I don't taste that in 1970s Dunhill blends nor Mac Baren Vintage Syrian.
I did smell Onyx and a jar of McClelland Cyprian Latakia from 2017 side-by-side and I would say the character was similar, so if someone held a gun to my head and made me guess, I'd say the Latakia in Onyx is now Cyprian, but that's barely more than speculation. One thing that I know for certain is that Schürch Onyx is a very fine and tasty blend.