I don´t know specifically about the DU 440, but on the fully adjustable shocks with external gas canister (the proper english word eludes my right now) I´ve worked on, the system looks like this:
P6290024 by
torbjörn bergström, on Flickr
The crosspin runs in a slot in the shock shaft and "clicks" against the serration in the bottom of the adjuster knob.The adjuster pushrod rests against the crosspin, and is pressed against the crosspin by the internal gas pressure.
Usually the crosspin bottoms out after maybe 40 clicks, but the adjuster knob can turn several turns more before it bottoms out against the mounting eye (i.e., no clicks).
I´m not familiar specifically with the DU440, but I think it´s the same type shock as other DU46´s.