Truth is conserved in consistent systems. Consistent systems are those which do not produce any contradictions by internal logical inference. It is obvious that any consistent axiomatic base produce a consistent theory in which true statements remain true regardless of new theorems and conclusions. Less obvious but still easy to see that true statements remain true even if the system is expanded by new axioms or other statements that are not derived within the current theory as far as the expanded system remains consistent.
Interesting implication of this line of thought is that a person retaining consistency of hir views is not able to learn new facts contradicting hir system of beliefs even if the facts seems to be true. To change view one has to accept many contradicting to the current beliefs facts in order to build a new consistent outlook and reject or reassess old known facts. For example, if a particular view is supported by ten known facts, another hundred new facts are not able to flip over the view because each of new facts is rejected due to contradicting to the current view hence breaking the consistency.
Therefore as long as one maintains hir set of beliefs in consistency, truth is never going to change.