Boundary between Baltic and Western MD should be one hex south. This errata was collected from email correspondence with Columbia Games . However, some hexes have tiny bits of land in them. These are not playable. There are also some anomalies where there are two unconnected pieces of land in a hex.
Most cases are common sense.
Riga NW2, NW3. Neither are connected by land to each other or the mainland. The hashmarks divide the AGN, AGC, AGS area north of Hungary. See list above in Map Section of Errata. Lake Ladoga and Lake Onega have impassable hexes.