After a few more hours reading the specifications and the post about versioned folders I realized I misunderstood the use of VERSIONED_OBJECT. I missed that a single VERSIONED_COMPOSITION is a container of versions of the same COMPOSITION template.
I missed that there is a “Problem List” archetype. I thought that a “Problem List” can contain different COMPOSITION archetypes. The actual model is that the openEHR-EHR-COMPOSITION.problem_list archetype can contain any other archetype.
Other persistent compositions listed in the specifications also have archetypes similar to the “Problem List”.
Thank you for your patience and explaining to what comes natural to you (with 15-30 years of experience) 
Special thanks to Thomas for his short answers that didn’t make sense to me (until I figured everything out) 
They kept me digging into the specs.