Various parts of the United Nations (UN) system have been part of the definition and implementation of technical cooperation among developing countries (TCDC), South-South cooperation (SSC) and triangular cooperation (TrC) over the years since the Buenos Aires Plan of Action of 1978 (BAPA). This paper will take the view that there is a perception that South-South and triangular cooperation have not achieved their potential to be transformative because accompanying changes needed for the modalities have not been pursued fully and thus these development modalities seemingly remain largely cosmetic. To respond to this perception, the authors will review what was expected of the United Nations development systems (UNDS) from Bandung to Buenos Aires and what has been achieved since noting the constraints of lack of data and measurement.