Doing a bit of research brought me to this old topic and here`s my two pennorth. I have a CD engine fitted with the screw in/out COV, the engine has no facility on the block for fitment of the usual lever which operates the COV so I would assume this was a production variant or the screw in/out COV is a replacement for a solenoid operated COV.
The halfway (decompressed) position on the usual COV fitted to CD CE engines in my experience makes for difficult hand starting, due to the restriction of the COV valve and as JP2 says, its not a problem cranking on full compression ( you need to start this cranking at TDC firing stroke) as the flywheel mass helps the first bump and subsequent bumps over compression.
Mark.