BBRC has, for many years, published records of birds identified as belonging to a pair or group of rare species, where the taxa involved are species that would individually be considered by the Committee but are confusingly similar or difficult to separate, even when the observer has obtained excellent views and as detailed a description as is reasonable under field conditions. This short paper, which complements Stoddart & Hudson (2021), gives the full list of species pairs and groups currently considered by BBRC, with reasoning for their inclusion. A discussion on some of the difficulties inherent in this ‘either/or’ approach is also given. Future updates to the list presented here will appear online at www.bbrc.org.uk/about/constitution/appendix-iv-species-pairs