As if determined to be the exception that proves the general rule, David Zinman closes his very fine Mahler cycle, one of the finest on disc in recent years, not with a recording of Cooke's version of the 10th, but with what was the earliest of all attempts to make a performing continuity of Mahler's final work by the American musicologist Clinton Carpenter, who began his "completion" in 1946 and finished it in 1966, though it was only performed 17 years later. It's a far more interventionist version than anything Cooke attempted, with textures regularly thickened and extra instrumental voices added, as Carpenter tries to second guess what Mahler might have added to the torso had he lived to see the symphony through to performance.
It's all entirely speculative, of course, but the main problem with Carpenter's version seems to me the fact that a number of passages just don't sound convincingly like late Mahler at all – the harmony has been enriched too much and the instrumentation bulked up, so it often seems like a step back from the spareness so characteristic of the sound worlds of the Ninth Symphony and Das Lied von der Erde, the other two works left unperformed in manuscript at Mahler's death. As you would expect, though Zinman and his orchestra play it wonderfully, and their accounts of the two movements that were completed, the opening Adagio and the third, the Purgatorio, are superb, but otherwise Carpenter's version can't really be recommended to anyone wanting a recording of Mahler's final musical testament.
