Composers exhaustively represented (i.e. virtually every recorded work with major/favourite pieces in multiple versions, if not every recording): Stravinsky, Britten, Tippett, Walton, RVW.(I don't do databases, but taking into account lp as well as CD, Le Sacre is the most prolific work of all - over thirty versions: the only two I regret buying are the Gergiev (I think I can understand what he's trying to do, but it doesn't work for me at all), and the Solti lp: so hard-driven and fast that paradoxically it loses power and momentum completely. The Tallis Fantasia isn't far behind for multiple editions, and most of the RVW symphonies are there in every recorded version.

 Composers with specific works or genres well represented: Shostakovich (four complete symphonic cycles, though fourteen recordings of the Fourth Symphony in total, eight of the Eighth and, perhaps more surprisingly, seven of the second): Grainger (eight Lincolnshire Posies, and several other works more than five times); Panufnik (not a large recorded output, but pretty well complete, including four performances of the Sinfonia Sacra. Save for the elusive Chandos recording of the Fourth Symphony, I'm doing quite well on Roberto Gerhard, too. John Adams and Steve Reich seem to dominate the American shelf, though Bernstein, Harris and William Schumann are also quite strong.

This probably makes the collection sound rather unbalanced, which in some ways it is, being centred around the early to mid C20th, but these anorak stashes are just blips in the larger collection which contains plenty of composers and works with few or even single works recorded, and I've not taken into account the huge number of off-air recordings amassed over the past forty or so years, which tell a slightly different story...

FMJ

No two-piano versions, but:

Fennell x 2 (Eastman Wind Ens., Mercury: Cleveland Symphonic Winds, Telarc)
Wick (London Wind Orch., ASV)
Banks (Central Band of the R.A.F, EMI)
Rattle (CBSO, EMI)
Westbrook (UCLA Wind Ens., Phœnix)
Hunsberger (Eastman Wind Ens., Sony)
Reynish (RCNM Wind Ens., Chandos)

And as a whacky adjunct:

Home Service (on the album Alright Jack Fledg'ling Records FLY 1001) make a creditable attempt to return the piece to its folk roots: wonderful stuff, rather analogous to the Pokrovsky's take on Les Noces! So 8.5 versions, I guess.

I'm very taken with The Lonely Desert Man Sees the Tents of the Happy Tribes too: not to mention The Immovable Do and The Warriors and that other piece of barking madness, the Scotch Strathspey and Reel, which never fails to raise my spirits, although it has to be the Britten version...

(Is that one of the Cornish NG lines, BTW?)

T9's especially, FMJ: Drummond built such wonderfully elegant loco's.

Quite by chance, I was at another NG line this weekend: same gauge, but a rather bigger beast....

Well, there's Grainger's Arrival Platform Humlet,which I have only once...(a feeble excuse to smuggle in a second shot: sorry Parsifal. I'll get back on thread after this.)

I have three recordings - Ian Brown, Richard Rodney Bennett and Kathryn Stott. None is ideal; Ian Brown is too Hyperion-clinical for my taste, but the wind playing is lovely - lots of character. Kathryn Stott is fast and loose (not necessarily at the same time) and the recording quality is pretty poor - the least of the three, IMO. RRB - mostly his playing is good, I think, a sort of middle ground between machine-like precision and  - well! - the opposite! But the orchestral playing leaves much to be desired, esp from an ensemble point of view.

The definitive performance is yet to come

Favourite Rio Grande is the one with Kyla Greenbaum and Gladys Ripley conducted by Lambert - it's on a Pearl CD with his arrangement of the Dante Sonata for piano and orchestra with Louis Kentner, and bits of Horoscope. (Lovely score)

There are still a few gaps in my collection - no Dirge from Cymbeline - have you heard that one?

Agreed ! Of those three, I only possess Ian Brown, who's not bad, but hardly characterful. I also picked up Alessandro de Curtis with Harmonia Ensemble which is pretty dreadful. I have a radio version by David Wilde from the 70s which is the most satisfying - unfortunately the cassette's on the way out . . . Favourite (by far) Rio Grande is same as yours with Kyla Greenbaum.
I've not heard the Dante Sonata orchestration - must look out for that CD. And I don't know the Dirge from Cymbeline. I imagine my Lambert collection is considerably smaller than yours - a couple of things I've never heard include the Prelude to Horoscope (allegedly clairaudiently written by Van Dieren) and a reasonable performance of Elegaic Blues. Apparently Lambert recorded it . . .

Only 44? IRF, that's nothing. These four CDs on the Trikont label

contain 83 versions of La Paloma by almost as many artists, spanning the entire world and the entire history of recording.

And yes, I have them myself. (Three of them anyway.)