I've been doing some testing. I've selected the 4 first pixels of the data (I ignored the hidden ones for calibration), for a .CR2 file (canon 5D), at 3 stages of processing: after unpack(), after raw2image(), after dcraw_processed(). See below (the 4 "channels" of the 2nd dimension are separated by the separator " | "):

user_qual = -1
imgdata.idata.cdesc = RGBG
unpack(): raw_image[ 0 ] = 2141
unpack(): raw_image[ 1 ] = 2098
unpack(): raw_image[ 2 ] = 2034
unpack(): raw_image[ 3 ] = 2084
raw2image(): imgdata.image[ 0 ][0 to 3] = | 2141 | 0 | 0 | 0
raw2image(): imgdata.image[ 1 ][0 to 3] = | 0 | 2098 | 0 | 0
raw2image(): imgdata.image[ 2 ][0 to 3] = | 2034 | 0 | 0 | 0
raw2image(): imgdata.image[ 3 ][0 to 3] = | 0 | 2084 | 0 | 0
dcraw_processed(): imgdata.image[ 0 ][0 to 3] = | 1576 | 0 | 688 | 0
dcraw_processed(): imgdata.image[ 1 ][0 to 3] = | 616 | 136 | 626 | 0
dcraw_processed(): imgdata.image[ 2 ][0 to 3] = | 0 | 132 | 371 | 0
dcraw_processed(): imgdata.image[ 3 ][0 to 3] = | 0 | 287 | 36 | 0

Why aren't the raw2image() values in the same column and instead, dispatched alternatively in the 0th and 1st column? Is that just to prepare the data for later demosaicing in a way that's compatible with all possible sensors? The values are indeed identical to the raw values. So it is unclear what happens between unpack() raw_image[] values and raw2image() image[][] values

Are the dcraw_processed() values dispatched in the 1st three columns to be considered as the R | G | B (and 4th is unused) components, after demosaicing?

Thanks