They probably won't get any better on their own. Perhaps now is the time to nip them in the bud with some discrete repairs as you mentioned. At the same time I would give a skosh of extra clearance at the back of the tang- make the relief below the visible surface of the wood leaving a RCH of wood on the surface to give the illusion of a tight fit.
I remain convinced that these cracks develop mainly from over tightening the draw bolt. Snug is good. Really torquing it down like your life depended on it is bad. Over tightening the bolt is akin to setting a chunk of firewood on Loggah's hydraulic splitter- those two wedges (tangs) are in effect constantly trying to turn the butt stock into kindling.
For a shooter gun with little collector interest, I would epoxy bed the whole shebang so as to spread the load over as much area as possible. I say that reluctantly though, for what is merely a shooter today may well be a rare gem 100 years from now.
