Circumstances do change, yes. But then I suppose what I most disagree with is your statement that “facts are circumstances that are changeable.” Facts may be circumstances, or circumstances factual, and circumstances may be changeable, but facts are not.
Think of it as it is a fact that circumstances were so and so at such and such time and place. Should circumstances change there will be new facts. But the previous fact will remain the same.
OK but to put it in you vernacular, there's no such thing as previous truth. Truth is the same, past, present, and future. That's the point.