There's a very long thread on cloudy nights about this (I can't find it right now though) and iirc there was quite a lot of sample variation in how strong the discontinuity is and how exactly it looks, non-uniformity in general seems to have a fair amount of sample-variation, though there are common patterns - like almost all sensors are fairly uniform for about 80% of the picture height and have a gradient towards the edges. Probably due to sawing, mounting or bonding stresses.

There are other causes for similar artifacts, e.g. banding because of mismatch between ADCs, though most CCD-based DSCs only used 1-4 ADCs interleaved. I believe some of the larger CCD sensors used separate read-out channels for quadrants, which would look similar to a stitched sensor in addition to likely being stitched anyhow. Also some Toshiba CMOS sensors had issues with banding due to mismatches between the column group ADCs. Lastly modern sensors for mirrorless cameras have split pixels for auto-focus in every n-th row, which also causes banding because they respond differently.