Nikolai Kirsanov has found in Ingria some placenames which have been borrowed from very early Slavic language:
"Abstract. Predecessors of Contemporary Russian y in the Toponymy of Ingermanland On the ground of certain conservatism in Finnic adaptations of imported Slavic place-names some reconstructions are presented of possible Slavic placenames of Ingermanland dated back to times before the first Slavic palatalization of velars (Finnish Kirnu < Church Slav *kir(s)nu black: cf Finnish musta black > Russian Mustovo and Russian Kornovo/Kernovo; cf Finnish Kuippina vs Russian Kipeń < *Kïpeń < Church Slav **Kuipini, where palatalization was impossible before a back vowel) and before the rise of ï from ū through ui."http://www.kirj.ee/public/Linguistica_U ... 07-3-5.pdf
(Article itself is in Russian, but the names and sounds are in Latinic. Kirsanov speaks about Old Church Slavonic, but it seems to be too late a language stage in this contest; see below.)
For example the names Kirnu
have been borrowed from a Slavic language preceding the first palatalization.
According to Frederik Kortlandt (http://www.kortlandt.nl/publications/art066e.pdf
) the first palatalization occurred during Early Middle Slavic, which ended about in the 5th century AD (see Kallio:)http://www.helsinki.fi/venaja/nwrussia/ ... Kallio.pdf
Here also Laukaa (in Ingria) and Väinä (River Dvina in Latvia) are presented as borrowings from Early Middle Slavic.
It seems that the Slavic homeland has reached from the Dniepr up/near to Olhava and Dvina basins - or at least some kind of colonies were there even centuries earlier than was earlier thought (maybe 300400 AD).