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if you have sbd/btc and btc/usd then you can calculate sbd/usd

It does not work exactly this way because you need to calculate one more commission in the process. This give you false information. Plus the trade volume at bittrex are very low

The commission on bittrex is only 0.25%.

Whether the volume is low depends on conditions.

Be cautious comparing volumes on crypto exchanges, because many exchanges and coins inflate their volume with sham trading.

Relatively low volume may indicate low interest, or just less sham trading.

I think it will be good if even those bittrex transactions will be shared in the post.

I don't think so

Today's SBD Price (Bittrex): 0.74 USD

While
Coinmarketcap says

$0.652090

The price on internal market seems to be around

$0.70

Coinmarketcap includes Upbit in their price calculation, but Upbit has not had a working SBD wallet for months if not longer. People are willing to sell there at a lower price because it is the only way to get their value out of the exchange. It doesn't indicate a market price for real SBD which isn't trapped there.

I would consider the Bittrex and internal market prices as closest to a fair market value.

If you mean excess rewards over the $25 cap, they simply aren't paid out and stay in the pool (to be used to pay other post/comment rewards).

If you mean excess rewards in the @sbdpotato fund when no longer needed to support the SBD peg, they will be donated to the Steem DAO aka SPS as stated in the post:

When the @sbdpotato funds are no longer required to support the peg, they will be sent to @steem.dao where the community can then decide what they should be used for.

Coin Marketplace

STEEM 0.28
TRX 0.12
JST 0.032
BTC 69731.54
ETH 3810.82
USDT 1.00
SBD 3.84