Thank you for the samples, most interesting.

A side note: in LibRaw we read Canon's metadata black level too, have a look at libraw_types.h, libraw_canon_makernotes_t -- it is in ChannelBlackLevel[4]. You can add something like
if (Canon.ChannelBlackLevel[0])
printf("ChannelBlackLevel (from makernotes): %d %d %d %d\n",
Canon.ChannelBlackLevel[0],
Canon.ChannelBlackLevel[1],
Canon.ChannelBlackLevel[2],
Canon.ChannelBlackLevel[3]);
to raw-identify and it will print those levels if called with '-v'.