There are Slavs in Northern Greece, but they are not those Slavs who spoke dialect used as basis of standardisation of OCS. What's so complicated about it?

you knowledge about the history of the Macedonian Slavs is based on guessing

they are the same ethnicity and are the decedents of the same tribes still  living in and around  the city of Solun

the Macedonian Slavs even today know the names of their tribes

if you are blindly supporting the greeks on the expense of the Slavs rename this forum to Greecvorum