Every time we were shown non-DS9 personnel in DS9 prior to the First Contact/Dominion War uniform, they wore the TNG uniforms.
Actually, no. When Quark organized the great darts game between O'Brien and the champion from the visiting starship in "Shakaar", the visitors also wore the DS9 style.
Possibly that style is the casual look or "B style" for small starships and informal occasions, and Picard ran a tight ship during TNG but loosened up a bit for ST:GEN? Note that our heroes generally change into the DS9 style in the movie when engaging in "work" (although not always dirty physical work) or having their "A style" uniforms soiled somehow.