Out-of-band rejection is attenuation through a stated path outside its passband. Duplexer isolation is leakage from a named source port to a named destination port with the remaining ports terminated and operating as declared. A rejection trace cannot stand in for every transmit, receive and antenna port combination.
Build a leakage budget: maximum transmitter level minus minimum transmit-to-receive isolation gives the residual at the receiver reference plane before other coupling paths. Compare it with damage, compression, blocker and desensitization limits, then include switches, circulators, cables, board and enclosure coupling.
Provide all port names, bands, simultaneous carrier states, antenna mismatch, temperature, power and switch state. Reject an isolation value without a frequency range, direction, terminations or dynamic-range margin. Verify every required S-parameter and the assembled front-end leakage path.