@reginasbread@tjanekane
I can't give numbers about your last statement, but I'm sure there are calculations about the shared vocabulary & gramm structures b/w Ukr-Pol-Rus etc (I supposed belarussian should be in the group too & Lith? & Let?) as there are for Scandinavian or Romance lang for instance.
As for the historical steps/dates u mentioned, I'd say they confirm a centuries long contact or common history of those territories.
I actually would just add it was there even before 🙂👍🏼