Memory Alpha wrote:
The Enterprise-A bridge is mostly a new set, except for the turbolifts, Sulu and Chekov's helm console, the handrails, and some of the platforms on which the portions of the bridge stood. According to the Collector's Edition DVD text commentary, a new bridge set was necessary due to the original movie bridge set being mostly damaged by a sudden windstorm while in temporary storage at the Paramount studio parking lot, and only those few pieces used on the Enterprise-A bridge were salvaged from the original set. Captain Kirk would thus seem to briefly break character when he muses, "I miss my old chair." The decoration from the salvaged set was also used for the Stargazer bridge and for the battle bridge in TNG.
Not really sure how the 2 stories combine, best guess is that maybe the main structure of the set had been altered to the point were it would be easier to just make a new one and the front sections which were unused in the Battle Bridge modification for EaF were the ones that were damaged in the storm.