I can understand the predicament. I was confused for a while too until I stumbled upon this ppt. I'm sharing the link here. This should help you I guess. Airbus clearly says you can interpolate for different limiting codes.
http://dream-air.ru/new/pilotam/WebC...AQ_takeoff.ppt
But the question which I've not been able to find an answer to is, how can we do an accurate interpolation when you are left with very little time to calculate as most of the time the trim and loading sheet comes in at the last minute. In such a scenario isn't it advisable to take the speeds for the higher take off weight because it can never happen that the speeds for a higher take off weight can adversely impact flight safety.
Say in a typical scenario suppose speeds for 52t are 113,129,134 and for 54t are 133,135,141 there's a wide spread between the figures and if I, in haste, erroneously interpolate for 53t on the lower side then I might not have sufficient stall margins for v2. Isn't it judicious in such a condition to take the speeds for higher weights?
Ssflying... Are you 'Nelly' by any chance?