Tolkien had changed the game a bit if Elfwine dropped out, for then he had Old English to help him with the Silmarillion.
Is Old English certainly out? Ach my memory...
I know the runes and letters in
The Lord of the Rings explain that JRRT translated the Red Book of Westmarch, but I would have to look at Appendix F more carefully to see if it's explicit that the translation went from actual Westron (and the ancient scripts) to modern English, with no help from an Old English translation.
I don't remember any Old English version mentioned in the context of the later 'Numenorean transmission' (or 'Imladris tradition' or whatever one might call it compared to the Elfwine transmission in general), but I mean is there something explicit enough that certainly rules out an Anglo-Saxon copy at some point?
I'll refresh my memory but someone will probably beat me to checking that out
I think I recall someone (Verlyn Flieger? Charles Noad?)
speculating that Elfwine could still play a part in the later transmission, at some point anyway, despite that he seemed to fall away, or ultimately seemed to give way to the Imladris and Bilbo notion.