Parece que pode ter dependido do tipo de ambiente em que o pessoal estava principalmente estacionado.
De Wikipedia :
throughout the run of DS9, ship-based Starfleet personnel continue to wear the old TNG uniform design. The new design may therefore have been intended as an alternate 'class' of uniform for the different environment of the space station, as in a scene in "The Maquis, Part I" Commander Sisko can be seen wearing the new style uniform while Commander Hudson can be seen wearing the old style. Sisko also wore the TNG uniform on certain formal occasions and during his first arrival at DS9 from the series pilot episode, Emissary. He would revert to this uniform again when he was temporarily given the duties of "Head of Security" for Starfleet Headquarters. Admirals also retained the TNG style.