Got lost in there somewhere. I'm saying the image data elements, as opposed to the metadata, are supposed to be identical. Which I think is what you are saying in the second paragraph.The data in the FITS file is not a bit to bit copy of the data in the ARW file, they are very similar but not identical. So these are different frames.
However, you are absolutely right: from the FITS file, crop 32 pixels from the right margin and you get the same image region as in the ARW file when opened with PixInsight.
out of curiosity was this master dark debayered or is this the raw CFA data?