I didn't read everything, so maybe this was mentioned or sidetracked. In any case, going off the OP SE increases weapon damage by 1 every 4 ilvls for the most part, but seems to arbitrarily round up or down at different times. This is the pattern they've used since ilvl 50 weapons (1-49 weapon damage scales differently) and holds true through ilvl135. If the next raid weapons are i155, for example, they'll have WD 62 or 63.