What I recall is that
Finrod used to be the name of
Fingolfin's younger brother, one of whose sons was named
Felagund.
Yep, that's the name-switch
Inglor Felagund to
Finrod Felagund -- but anyway, I was referring to
Orodreth becoming Angrod's son instead of his brother, as found in
The Shibboleth of Feanor for example, and
Tolkien's latest family tree (where it concerns this matter).
The introduction of
Finarfin (spelled Finarphin early on) postdates the first edition of LotR, with Finrod moving down a generation while retaining his "epithet" Felagund. It all had to do with JRRT needing to sandwich in
Galadriel somewhere in is
First Age mythology, where she had not existed prior to LotR.
The name switch appears to be based on Tolkien's concern (see
Words, Phrases and Passages, published in
Parma Eldalamberon 17) that the character "Finrod" should not have a
Sindarin or Sindarized name, as he hadn't left
Aman -- and ultimately JRRT gave the name to "Inglor" (
only called Felagund in print so far). Back to WPP, at one point Tolkien gave the former "Finrod" the
Quenya name
Arafinwe Ingalaure.
actually it's a bit more complicated than that, but for sake of brevity here
Tolkien then notes (still WPP) some Sindarized forms, writing
"Feanor, Ingolfin and Inglor (but this not actually applied to Arafinwe who never came to Beleriand)." Tolkien then notes how the name
Ingolfin arose, but adds a very interesting remark here:
"[If Fingolfin is used at all this must be for Finwe-nolofinwe]"
AHA! This little extra bit starting with "if" basically turned out to be the scenario as described in the later text
The Shibboleth of Feanor -- ahem, cough -- where Tolkien explains that
Sindarin Finarfin is similarly from
Finwe Arafinwe, and he explains why Finarfin,
even though he remained in Aman, received a Sindarized name!
Basically, between editions of
The Lord of the Rings, Tolkien is thinking about revising certain names in his mythology, and thinks that "Finrod" should not have a Sindarized name 'cause he stayed in Aman -- then, later, "he" [Finrod] ends up with a Sindarized name anyway: Finarfin!
Or something betterly worded by me!
🐾