If you find the CV643D description on the
The Big Book of Amiga Hardware page, you'll notice that there were 2 different CV643D versions made. 1 was by Phase 5, and the other by DCE.
In the description of the DCE card, there's a line that says that the only difference between P5 and DCE models was compatibility with Z4 A1200 board. P5 model lacked it, and DCE model supported it.
I guesss that could be the reason.
