There is SBD being created into the SPS treasury, which is counted as part of the supply (IMO this should be changed; I would only count SBD supply when it is paid out from SPS) but most of it isn't being paid out. Currently 280 SBD per day are being paid out from SPS (keychain $100 and howo $180 proposals) and potato is removing more than that (others convert too), so the circulating supply is shrinking even though the blockchain reported-supply is increasing.

I believe the total printing into the SPS is about 1500 SBD per day so potato will probably get to that at some point if its funds continue to grow, and then the reported supply will also decrease (may happen sooner due to others converting).