Does the reconverted DVD-Video data (from .RatDVD) always fill the target media (single layer and double layer)?
No. RatDVD always tries to reach the best possible video data for the size given. However, there may be cases where even with the best possible quality not enough video is available to fill the whole DVD. Especially when the target is 9GB double layer it will probably not fill the disc – but still have the optimum quality.