It sounds like a broken record, but it is important when overseeding bermudagrass to have as healthy turf as possible.  Research continues to find the healthier the bermudagrass is going into winter the better the spring transition.  If your bermudagrass is not healthy going into winter try to identify the reason and correct it (ex. too much shade, etc).  In cases where overseeding of weakened bermudagrass occurs, try to minimize mechanical injury as much as possible.  Weakened bermudagrass will not transition in the spring quickly if stressed during the autumn overseeding.