Don't worry and yes it could be fixed but difficult and would make zero difference in the house. Very common for wide boards to "cup" and it is based upon their grain.
I certainly agree with your statement but back when the reusing subflooring like this they definitely were not using construction adhesives. Lots of good nails pounded by hand instead of by nail gun but construction adhesives didn't even exist yet.Mine are like that too. You have to consider that at the top they could be glued and nailed to the subfloor and if you mess with them it could disturb the floor material above and give you a bigger problem.