Trust Me,
I am glad you said that, I had this argument with my Check Captain at my last simulator check. It was simply a Blue Hyd Failure and I took the Flap Full VLS out of the MCDU and added the correction, entered it in the FMGC and then selected Flap 3. He said that I must ALWAY's work out the V APP from the QRH and had no idea where I could have gotten the idea that taking it out of the MCDU was allowable. I told him that after flying the Airbus for 10 years I must have been mistaken on every other check and showed him the chapter in the Flight Crew Training Guide saying you could do this. He still wouldn't have it!!
In answer to the first question:
Vapp Calculation is the table to use for Abnormal / Emergency scenarios.
Vapp Determination is the table to use in Normal scenarios.