Being a surveyor, you wouldn't . If the corbelling was actually called on to do any work, it couldn't. The stack is hanging off the party wall and its ability to do that depends on the condition of the whiffs, which invariably are pants, due to long term action of the smoke on the mortar. The corbelling has added nothing whatsoever to the stability of the flue. If you were doing a survey and gave that a clean bill of health, then you're a braver man than me .As it is, I can't see a problem with the corbeling
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