circulating supply IS total supply. differentiation is meaningless, except maybe to point out that the supply cap is already priced into the fiat valuation.
we just have reasonable assurance the circulating supply inflation stops at 21M.
pretending that the block reward already existed somewhere before the block was mined and were simply "released" is just semantic slight of hand so people can say "Bitcoin doesn't have supply inflation"
the point is that Bitcoin depends on supply inflation to pay miners to secure the network. as long as you and I are alive, miners are "robbing" us of our stored value by diluting the supply.
which is true.