Hi Steven,
Your crew may well have been planning to depart from an intersection, probably Golf. ATC like to have access to a range of aircraft departing in different directions, so crews will often offer an intersection departure when Northbound in case the holds at the full length are full of Southbound aircraft. The reduced Take off distance available may well necessitate the use of conf2 or 3.
If the crew subsequently depart from the full length, they can either switch to the related performance, which may involve flap changes and some heads down FMGC programming; or use the previously loaded figures on the basis that they were for a shorter TORA, TODA and ASDA. Many will choose the second option in order to avoid the threat of making an error. As it happens, perf figures for 08R are quite often based on conf3 in a 320.
HTH
Smokey