You are right that both these names relate to the same species.
Don’t forget that the Species Dictionary is a collection of checklists and aims to represent names exactly as they are presented in various lists.
Thus we have [i]Aceria fraxinivora [/i](without an authority) NBNSYS0000050406, which comes from the Recorder 3.3. list; [i]Aceria fraxinivora [/i](Nalepa, 1909) NHMSYS0020190408, which provides the well formed name, was obtained from the Fauna Europaea list of Prostigmata of Britain (this list was imported to fill a significant gap at that time; [i]Aceria fraxinivorus [/i](without an authority) NHMSYS0020470049 is in the British Plant Gall Society checklist.
All three are mapped to [i]Aceria fraxinivora [/i](Nalepa, 1909) in the Name Server, and [i]Aceria fraxinivora [/i](without an authority) and [i]Aceria fraxinivorus [/i]are marked as ‘ill-formed’.
I also sometimes despair at the multiplication of names caused by such variants. The Species Dictionary (in the main) does a good job of mapping equivalencies, but I appreciate that equivalencies may not be so easy to spot in the way lists are presented in Recorder.
We are currently rebuilding the Species Dictionary website at the NHM and, when finished, this will make it much easier to find out which is the recommended name for a species.
NBN Species Dictionary Project Manager (Retired!)