No, the "5 sons" references are in quite a late text, written after the story about one of the sons dying on the burning ship was written. The seven sons of Fëanor go back literally to the beginning of the development of the legendarium in the Lost Tales. The 3 references to the "5 sons" are all in what Christopher describes as follows:
On another page is the following long, rapidly written, and remarkably elaborate discussion of the motives of Celegorm and Curufin
The references are all bunched together:
Curufin of course knew well of Eöl's hatred of the Noldor, and especially of Fëanor and, as 'usurpers' (though in this case unjust, since the lands occupied by the 5 sons had not been peopled before by the Sindar). Also he knew of Eöl's friendship with the Dwarves of Nogrod (indeed Eöl could not have journeyed alone across E. Beleriand to Nogrod unless allowed by the 5 sons), among whom he had tried with some success to stir up unfriendliness to the Noldor. Which was a grievance to the 5 sons, who had, before Eöl's coming to Nan Elmoth, had much profit from the help of the Dwarves.
Christopher notes:
It does not seem credible that the Seven Sons of Fëanor, so deeply rooted and so constantly recurring in the tradition, should become five by a mere slip of forgetfulness, as in the omission of Fingolfin from the genealogy
I don't know that I fully agree with this. When Tolkien wrote rapidly, he did often make mistakes. Certainly, omitting Fingolfin from the genealogy is as egregious as referring to 5 sons instead of 7.
"Spirits in the shape of hawks and eagles flew ever to and from his halls; and their eyes could see to the depths of the seas, and pierce the hidden caverns beneath the world."
