Damage to leaves doesn't heal. As long as the new growth is ok, you've probably fixed the problem. Time to get a new pH meter.
If rockwool has been flushed out well before use, it won't have much effect on the system pH. Residual limestone dust in rockwool from manufacturing can cause pH to jump up.
If rockwool is well flushed before use, the pH you measure in your tank is pretty much what the plant is seeing when exposed to the same solution in the rockwool.
I flush my cubes and
soak them for a day before using them. However, I use rockwool floc (loose rockwool resembles bulk fibreglass insulation) in pots in my flood system. There's so much of the stuff in my op that it's just not practical to fully flush it nor soak it. I just run my tank pH a little lower than normal to compensate for the slightly alkaline rockwool floc, around 5.2-5.7.
If you only have a couple of weeks to go, I wouldn't muck around with it much. If in doubt, plain tapwater is a lot closer to right than a solution which has been corrected without good pH measurement tools.