Sometimes, it is necessary to know details //about// a statement group. Unfortunately, Wikibase does not provide a way to do this.
[[ https://www.wikidata.org/wiki/Q156229 | AK-74 ]] has two statements with [[ https://www.wikidata.org/wiki/Property:P607 | conflict ]] as the property. Is this list a complete list or an incomplete list? Wikibase's current data model makes it impossible to reason the completeness or incompleteness (or any other properties for that matter) of a statement group.
This makes questions like: "In which wars in the 21st century was the [[ https://www.wikidata.org/wiki/Q156229 | AK-74 ]] //not// used?" impossible to answer.
Perhaps when statement groups need properties, an intermediate object (like [[ http://blog.schema.org/2014/06/introducing-role.html | schema.org's Role ]]) could be added so those properties can be added to the statement group itself.
# A common work around on Wikidata is to create another property that has the //count// of items. For instance [[ https://www.wikidata.org/wiki/Property:P2437 | number of seasons ]] and [[ https://www.wikidata.org/wiki/Property:P4908 | season ]], the former informing the completeness of the latter.
# Another common workaround is to create [[ https://www.wikidata.org/wiki/Q12139612 | list ]] items like [[ https://www.wikidata.org/wiki/Q52105174 | reasons for deprecation ]] that could have a [[ https://www.wikidata.org/wiki/Property:P2429 | expected completeness ]] property