@erikvannieukerken it seems this change is not to the species 'Stigmella salicis', but to the 'Stigmella salicis complex', i.e. changing it from a 'group' to a 'complex' (and is one of several such changes). Nevertheless, I cannot see why this change needs to be made as 'group' is a standard term used by taxonomists and a species complex usually refers to a small number of difficult-to-identify known species. Moreover, in iNaturalist the use of 'Genus species complex' can be very confusing as in some situations one only sees 'Genus species', as in the Stigmella salicis example here. Only once it has been clicked or selected does it appear as 'Genus species complex', It should have been left as 'Genus species group'.

Yes, that is what I mean. A 'complex' is not used in the same way as a taxonomic 'group' and I am not surprised you have a Stigmella salicis complex among the Stigmella salicis group.