Why 1D00FFFF and not 1CFFFFFF as target in genesis block

In the custom uint256 encoding used in Bitcoin, bit 0x00800000 denotes the sign, so 0x1CFFFFFF actually denotes the value -2²⁰⁰(2²³ - 1). Obviously the target value cannot go negative, so this aspect of the encoding is not useful in this context, but for whatever reason, that's what Bitcoin's creator chose.

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