Deryk Barker:

>Does anyone know anything about this?

Charles Mackerras recorded "the Initial Performing Version of the Slow
Movement", I believe this is what you've heard.  It is on the Telarc
disc with the first symphony (which is - as the whole cycle not particularly
commendable, due to the utterly poor horn playing).

>I wonder who did the reconstructiuon (and when) and why it was necessary.

While this isn't clear in the Telarc notes, I believe it to have been
made by Robert Pascall.  As to why, he writes: "Altogether these changes
provide a deeply fascinating insight into genius at work." To me, this
sounds like the usual "wahoo, we found something by a known composer,
let's call it the greatest thing ever", similar to Beethoven's tenth or
the Bruckner 9 finale. Of course, this "unique" view into a composer at
work is familiar from BIS' busy unearthing of Sibelius sketches.

Jan