I'm not going to copy paste CS25 as it's available free for download.
Vac has no relation to V2. It may be that some manufacturers have tied the two together but each is independent and has it's own requirements. Some aircraft go around with flap settings not available for Take off and as such there is no V2 schedule for the configuration.
Landing climb is 3.2% all engines operating landing flap and gear down. This may limit Vref to a speed higher than the minimum stall margin. This is the case for the Ejets with flaps Full. So much drag that to make the landing climb requirements they had to increase the Vref speeds.