Yes, smittims, the ABQ (as they're now often called) have played at the South Bank Centre (or the Southbank Centre, as it's about to be re-christened
) in most recent seasons I think. I don't remember what was their most recent recording but it's certainly later than 1991.
Rits at the end: depends on the performance style, doesn't it? It could happen, in certain music and in certain performing styles, but I doubt many conductors today would behave like Sargent in your story. Or imagine what a mess the end of Sibelius 5 would be if ritardandos were universal practice at the end of a work!