And a couple more:

Michael Tilson Thomas taking over from an indisposed William Steinberg
in the midst of a Boston Symphony concert at New York's Philharmonic
Hall in October, 1969--one month after being named BSO Assistant Conductor.
Although passed over in favor of Ozawa when Steinberg stepped down,
Thomas went on to success in London and, now, San Francisco.

Colin Davis' rapid ascent during the 1959-60 season, paying his dues
with an acclaimed opera series at Sadler's Wells, then substituting for
Klemperer in concert versions of Don Giovanni with the Philharmonia at
Royal Festival Hall.  Subsequent notices proclaimed him the "new Beecham."

Dick Claeys