Feanor Self-Important?

[the phantom]

You know, SP, even though I don't agree with the interpretation I'll try to answer your question anyway.

When Mandos says "Not the first" it means "I don't know what I am talking about." I mean, if Feanor is the first but Mandos says he isn't, Mandos is in error, right? I guess he has Feanor's birthday marked wrong in his datebook. That's probably why, after Mandos says his line, the book says-

but they did not understand his word

Because he had his dates mixed up.

Yet another illustration of the Valar being wrong. Yes! Maybe I should buy into this interpretation after all.