Models of stellar evolution constitute an extremely powerful, and for the most part apparently very successful, tool for understanding the progression of a star through its lifetime as a fairly compact entity of incandescent gas. That success has led to stellar evolution theory becoming a crutch when an observer is faced with objects whose provenance or current state are in some way puzzling, but how safe a crutch? The validity of the theory is best checked by examining binary systems whose component parameters have been determined with high precision, but it can be (and needs to be) honed through the many challenges which non-conformist single stars and triple systems also present. Unfortunately the lever of observational parameters to constrain or challenge stellar evolution theory is not as powerful as it could be, because not all determinations of stellar parameters for the same systems agree to within the precisions claimed by their respective authors. What are the sources of bias—the data, the instrument or the techniques? The workshop was invited to discuss particularly challenging cases, and to attempt to identify how and where progress might be pursued.