I'm away and don't have access to the code(I just remembered the GitHub, though the versions don't quite match). There is a nightly chance to restore tightness, though there are 2 RNG checks. The details are found in expansion.gd in func dailyTighten. There is an option accessible by Constants(vaginaltightenchance), though it simply changes the base chance with an age multiplier. It is affected by the new trait for elasticity.