Halliday & Matthiessen (2004: 548):
The conjunctive relation of ‘matter’ is very close to some of those of the elaborating kind, and the concessive (‘despite X, nevertheless Y’) overlaps with the adversative (‘X and, conversely, Y’). Such pairs are characterised by differences of emphasis, and some instances can be assigned to one member or the other; but others cannot, and may be interpreted either way. As always, we can try to bring out the most likely interpretation by checking close agnates to examples occurring in the text.