[Taxacom] is different ending for gender a synonym

[John Grehan]

I'm compiling synonyms for species in a taxonomic list and I am curious to
know if there is a standard view of what happens with different
gender endings - whether they are considered synonyms that should be
listed. For example, Moschler 1826 named Epialus hyperboreus which was
later transferred to Gazoryctra as hperborea - presumably to match the
gender, but then later the species was listed by the same author along with
some others (Nielsen et al 2000) as  Gazoryctra hyperboreus,
reflecting their view that species endings should stay with the original.
I'm not worried about arguments over that choice, but whether these names
are formal synonyms. Nielsen et al (2000) did not list hyperborea as a
synonym, but I noticed that it was listed as a synonym on a taxonomic
website  https://ftp.funet.fi/

So, is there any formal criterion or is it just a matter of personal
viewpoint as to whether the different endings constitute synonyms?

Thanks for any input on this.

John Grehan