I guess I’ll answer my own question. For those that are interested:
browsing through the pdf manual of the DMR-BW900, I found out that these are constantly grouped together:
HDD; BD-RE (ver 2.1); DVD-RW (VR); DVD-RAM. I’m assuming if you record to these, editing features are allowed.
-RW (V) is its own animal.
then BD-R DVD-R DVD-R DL (discs you can/must finalise).
Interestingly, I don’t think BD-R DL is compatible at all with these machines.