It would be helpful to have more information on the use of bf:mainTitle as opposed to rdfs:label.
The Titles specification (https://www.loc.gov/bibframe/docs/pdf/bf2-titles-apr2016.pdf) uses both in the examples. Specifically, examples 2-5 use bf:mainTitle to hold the title string. It seems that examples 1 and 6 could as well. The definition of bf:mainTitle is quite broad: “Title being addressed. Possible title component”.
Alternate Example 1:
a bf:Title , bf:WorkTitle ;
bf:mainTitle "Reflexive interpreters and autobiographical texts" ] .
Alternate Example 6:
a bf:Title , bf: VariantTitle ;
bf:mainTitle “Chartbook on aging” ;
bf:variantType “spine “ ] .
What are the criteria for using bf:mainTitle vs. rdfs:label?