When the Count Basie Orchestra first achieved prominence in 1936 it was using a basic antiphonal style and repertoire borrowed from other performance groups.
In those days, the originality of Basie’s orchestra lay in its rhythm section and in the abilities of its several outstanding soloists. In effect, Basie brought a version of the Kansas City backroom jam session onto the bandstand.
When he re-formed his orchestra in 1950–51, after over a year of leading a sextet, Basie depended on mass effects, orchestral precision, adventurous voicings, and a new repertoire.
During this time he relied on the talents of composer-orchestrators Frank Foster, composer of Shiny stockings, Neal Hefti (Cute), Thad Jones (Speaking of sounds), and others. Basie’s new sound slightly echoed that of the Jimmie Lunceford Orchestra of the 1930s, but was otherwise without precedent in jazz history.
This according to “Horses in midstream: Count Basie in the 1950s” by Martin T. Williams (Annual review of jazz studies II  pp. 1–6).
Today is Basie’s 110th birthday! Above and below, the Count Basie Orchestra in 1951 (pictured above with Ethel Waters).