Mitochondrial Complex I is the first and largest holoenzyme of the mitochondrial electron transport chain. It oxidizes NADH from the tricarboxylic acid cycle and β oxidation of fatty acids, reduces ubiquinone and transports protons across the inner membrane, contributing to the proton-motive force. It is also involved in the cellular production of reactive oxygen species. 'Accessory' or 'supernumerary' subunits are all encoded by nuclear DNA and are not directly involved in catalysis. (Adapted from PMID:23527692 and FBrf0244962.)
The division between 'CORE' and 'ACCESSORY' Complex I subunits in FlyBase follows that given in FBrf0244962.
These nuclear genes encoding accessory subunits of Complex I exist as paralogs in D. melanogaster: ND-B14.5A and ND-B14.5AL; ND-AGGG and CG40472. In addition, CG11815 and CG12464 have the same InterPro domain (IPR026193) as CG11752 (a NDUFV3 ortholog, FBrf0244962), but no there is no other orthology/literature evidence suggesting they are subunits of Complex I - CG11815 and CG12464 are therefore not included in this group.