Three bits are used to specify condition codes: 000=NZ, 001=Z, 010=NC, 011=C, 100=PO, 101=PE, 110=P, 111=M. The JR instruction only decodes the 2 lower bits of the condition code.
Condition C (carry) is unrecognizable from register C (BC). To recognize which it is, conditions (flags) are used only in instructions: CALL, JR, JP, RET.
All CB-prefixed opcodes and half of the standard opcodes (from &40 to &BF) follow a strict uniform layout. The sole exception is the HALT instruction (opcode &76), which replaces the expected LD (HL),(HL) instruction.