So I think any of the 50 *could* be sold through the Sound Swap system, but only as liquidity permits; with more mints comes more liquidity comes more opps for the original 50 minters to sell back through. But if that liquidity gets depleted through sales you'd have to wait for more mints to replenish the LP, etc. Also, NFTs always stay in users' wallets but it's a portion of the ETH payments that are distributed to the pool, the fungible tokens.