Hi Cactusson, the ISAF does not actually measure the boards, they get a specification sheet from our supplier, who scans the final shape to get the volumes...not really 100% accurate. Our board volumes are calculated using a CAD system, so the nr on the board is really very, very close to the real volume.
if you want to compare sizing, then often better to check the widths and the nose/tail widths, as it´s not too often that thicknesses will change much. The 2018/19 was 63cm, vs the previous 62cm version. 2020 is now back to 62cm, but with a fuller, straighter outline. The key on this size for most PWA and National riders, is to make a board which is small enough for riding with a 5.6 in very choppy water, but then also to stretch it to a 7.0 when the 115 is too big. The 1cm bigger/smaller can be noticed, but it depends then also a bit on the total shape.
I would say 2016/17 vs 2018/19, you will feel the 1cm as an advantage yes, more just is sail carrying ability than pure volume/buoyancy.