I think I read somewhere that for most recent common ancestor you count back from 1950, something about nuclear tests causing a discrepancy or something. My R-YP445 also has a TMRCA of 1300 ybp, whom I've nicknamed 'Jaromar the Wendish Warrior', as he lived in a very early Polabian Slavic tribe that the Germans called Wends; today most of his descendants are Germans or have ancestors who immigrated from Germany. So, yes, I would connect that TMRCA to the Slavic expansions.