We did not know about close encounters between Germanic and Slavic tribes prior to the Viking Age. The recent discovery of runes on a Czech cow bone challenges that perception we have so far (see A Cow Bone with Runic Inscription).
Similarly, we do not know a lot about the West Slavs in Poland. Dr Leszek Gardeła challenges our perception about the interaction between Vikings and the West Slavs. Some Polish warrior graves dubbed ‘Viking’ might need closer scrutiny for West Slavic influences, though.
See Dr Gardeła’s paper on the ever-excellent Medievalists.net.