AFAIK there's a great deal of unpublished DSCH material, BUT it's mostly fragments, sketches, unfinished pieces, arrangements, etc (allegedly).  Like all composers in the soviet era, DSCH was obliged to turn his hand to almost anything given to him...  as well as material he wanted to write, there were all kinds of "tunesmith" tasks with which he got involved.  (I suspect that in part at least, he relished the prospect of tasks which he could get his teeth into without political interference, but this is only my guess).  For example, he did a large amount of editing - there's an entire version of Mussorgsky's BORIS GODUNOV which DSCH reworked and rescored.  It got a playing last year in the Anniversary beanfeast...  for the "Bells" which begin Act II, DSCH has scored for 18 percussionists!  And that's not to mention the four harps his score requires...   there are the tell-tale solo xylophone and snare-drum sounds, too.   But quite apart from the fantastical orchestration, he's mined the original resources to produce what's outstandingly the best dramatic version of the opera... managing to preserve the scene-order of the original Pushkin play (more-or-less) and get most of Mussorgsky's musical material out onto the stage.  The result is a revelation - Marina Mniszek (who doesn't even appear at all in the "authentic Mussorgsky original" edition by Lloyd-Jones!) is the centre of the action.  DSCH spots one of the main problems with the "original Mussorgsky" opera - it lacks a protagonist.  Things happen TO people, but no-one's causing them.  He also cranks Rangoni's part upwards (by a tone or sometimes a minor third).  It's a completely opposite approach to the painstaking scholarship of Lloyd-Jones - for Shostakovich, the aim is to make stunning music-drama out of the gloomy introspection of the "traditional version" - without adding a note.


Shuisky, Ksenia, Fyodor, Boris


Simpleton


Rangoni, Marina Mniszek


"Tsarevich Fyodor"

On top of all that, though, there are lots of fragments lying around.  I saw a show in Moscow last year performed by Boris Pokrovsky's Moscow Chamber Opera,  made-up entirely out of unpublished fragments.  In fact a lot of them were material we already knew - a first draft of the second movement of Symphony 14,  some of the songs.  But there was also a lot of unknown material,  although I wasn't always convinced that the relentlessly gloomy scenario (devised by Moscow Chamber Opera as a vehicle to mount these fragments) of a Gulag-camp political prisoner was necessarily appropriate to them.

The entire situation is complicated by an ownership dispute over much of the Shostakovich Archive.  A large part of it ended-up in Tallinn (now the capital of independent Estonia) during the USSR period.  The Estonians are refusing to part with any of it, or even allow Russian scholars to access it,  and it's been kicked into touch as a political football between Estonia and Russia.  Since Russo-Estonian relations are at the lowest imaginable level currently (for reasons entirely unlinked to Shostakovich, ehem!) it's hard to see this situation improving much very soon. 

As well as the composer's wife's bottom drawer, there is also believed to be substantial material amongst Rostropovich's papers (guarded assiduously by his widow currently), and amongst those of Galina Ustvolskaya (who died at the end of the centenary year of her one-time mentor).

There was a talk on this by Olga Digonskaya who was billed as from the Shostakovich Archive in Moscow (is that more or less 'official' than the St Petersburg one that Reiner mentions?) at last year's* Goldsmith College Centenary Conference thingy on Shostakovich. She mentioned large quantities of new documents, drafts, working papers etc which were coming to light, many in private hands, but I don't remember her dangling the prospect of anything very major in the way of unknown new works. But things may have changed since then of course. 

[* Oh God, it was the year before last wasn't it. This time compression business is getting terrifyingly worse.]      

I fear you're right - if Mr Matsov (who is clearly "building-up his price") knows there are any juicy large works remaining in manuscript, he's keeping unnaturally quiet against his own interests.

That's enticing news about URANGU, Reiner. Thank you for that

THE SILLY LITTLE MOUSE does seem to exist in full score form http://www.boosey.com/pages/cr/catalogue/cat_detail.asp?MusicID=5897 and, since there is no indication to the contrary, I assume it is the original scoring rather than a reconstruction (?). It did get at least one performance here during the DSCH centenary year at a Prom at the Cadogan Hall, so not entirely forgotten. The film itself was also given an airing at a 'Shostakovich on Film' festival at the Barbican that year so a copy of sorts exists. Maybe someone here saw it (I didn't ).

Thanks, George!  The info that the full score is lost comes from my piano-score copy of SILLY LITTLE MOUSE, so I am glad Boosey's have something a bit better?   If a copy of the film has really survived, it wouldn't be impossible to recreate the orchestration from the soundtrack anyhow

Soviet animation was quite advanced, so I presume the film might have been rather better than the reviewers claimed? 

The storyline is quite simple - Silly Mouse won't stop crying, so his mum asks different people (Auntie Duck next-door, Mrs Pig, Mr Toad, the Pike-Fish etc) to sing him to sleep.  But Silly Mouse is just rude about their singing and continues to cry.  Finally Mrs Cat offers to "deal with" Silly Mouse, but Polkan intervenes just as Mrs Cat is adjusting her bib and tucker.

There's a short video clip of the Bolshoi production of BOLT  ("The Saboteur"), here, by the way:

http://youtube.com/watch?v=eJZ6dzqlUvY

It's only the overture, with the opening credits, but it gives you something of an idea of the piece, anyhow

Excellent, GG - thanks for finding that one!!