Gharib concerns limited numbers of transmitters at some point in transmission. Shadh concerns a report that contradicts a better-established version. Therefore, not every gharib report is shadh, and shudhudh is not merely another name for rarity.
Case 1: An upright, precise narrator uniquely reports a text, there is no stronger conflicting version, and the remaining conditions hold. The report's uniqueness alone does not disqualify it.
Case 2: A generally accepted transmitter contradicts a superior, demonstrably preserved account from the same transmission setting. The inferior version may be classified as shadh.
Summary: gharib describes the configuration of routes; shadh in this discussion requires conflict together with relative inferiority.