If often works fine.
When the "adding mechanism" cannot continue to build, then create another new empty target collection and continue with that.
That way you may end up with several collections which match quite well internally.
It may then be possible to crossdate these collections towards each other and hopefully also add all
their members together.
There is information and examples on collection building with CDendro at
- http://www.cybis.se/forfun/dendro See section 7. Rebuilding a collection
http://www.cybis.se/forfun/dendro/hollstein See "Rebuilding the Hollstein chronology"