Hi there. STEEM and STEEM POWER are still both STEEM. So by moving from STEEM to SP this doesn't affect the Supply of overall STEEM tokens. If you simply sold SBD on the market for STEEM again you have not affected the supply. It seems token supply is affected only when SBD holders use this quirk - the "SBD to STEEM Conversion mechanism" where it cancels the SBD and creates new STEEM. I hope that makes sense - there is a lot of complexity in this - and I am still building my knowledge on the topic the more I ask questions and read up on it too!