I don't think the issue is continuity itself (as RAC points out), it's more a case of writers looking for handy elements to tie their story into the Dredd universe and give it relevance (thus dodging the hateful fanboy term 'filler') without pointlessly tinkering with the character of Joe Dredd or altering the MC-1 status quo too much. We have an odd situation with the Dredd strip where all rightly defer to Wagner's vision, since even when he's not writing it's not like he's passed the baton to any one writer, but where so much that is good has come from other creators.
It's a grounding counterpoint to the business of introducing your own characters and long-running plotlines. Looking at Young Master Carroll, you can see the way he's pursuing these two directions: his East-in-the-West MC-2 Sovs sequence being his own, and his Dolman: Clone in the City stories depending much more closely on existing Wagner elements.
It's playing with the toys already in the Wagner sandpit as well as your own, rather than digging a giant hole and burying everything (you can tell I'm looking after kids in the sunshine, can't you).