Three Great Unfinished Symphonies

[Wanderer]

In my view, Schubert's Eighth is the only one among these three that's truly unfinished. For performance purposes, I do not consider Mahler's Tenth to be unfinished (for all the reasons already mentioned above and in previous conversations we've had here and in the old forum over the years) and, with the available completions, Bruckner's Ninth is as unfinished as Mozart's Requiem.

[Jo498]

If one buys into the Rosamunde b minor entr'acte as finale Schubert's 7th/8th might count as the most complete of the three! But this is of course some stretch. In fact it was the only one left deliberately unfinished because this was apparently Schubert's way when he got stuck. It was apparently faster for him to start and complete a new piece (such as in the (I think) D 845 vs. 840 piano sonatas (a fragment as great ad the b minor symphony)) than to re-draft, edit etc. to complete a piece he had become stuck in.
I think it is probable that the most complete was actually Bruckner 9th, if the "friends" had treated the draft of the finale in a more careful fashion.

As for Mahler's 10th I have to admit that I don't know the work as well as many others here. But for me it does feel (in the common performance versions) that it gets more sketchy in the last 2 movements. And the first movement feels far more complete than 2 + 3, so I am not really convinced by the whole thing.
I also find the setup with the utterly strange, oddly titled and tiny "Purgatorio" in the middle sufficiently puzzling that I could imagine Mahler making more changes than mainly completing the orchestration.