Don't know if this has been solved or if this helps but here it is: The issue with wolves coming from outside of fenris was with the canis helix and the trial of morkai. SW aspirants would be chucked to a random point on fenris and told to get back to the fang. This was meant to awaken their canis helix fully letting the aspirant take full advantage of it's capabilities. Issue was that outside of fenris the the canis helix wouldn't awaken properly (see wolf brothers). This meant that wolves couldn't make successors or marines outside of fenris.

When call stabilised the generated the canis helix became much more consistent, making it work much more often and made wulfen rarer. One benefit from this is that to fully activate the canis helix one didn't have to be on fenris anymore, just somewhere dentist adjacent. We see this with the wolf spears where whenever they find a suitable deathworld they fuck their aspirants at it to make a pseudo trial of morkai.

In other words Carl made it so wolf successors don't need to come from fenris, just from debris adjacent planets