Ishikawa--Shimokawa conjecture on finite boundary slopes

Let $K$ be a knot in $S^3$, and let $b$ be a finite boundary slope for $K$.

Ishikawa--Shimokawa conjecture. Then

$$|b| \leq 2c(K).$$

This follows immediately from the boundary slope diameter conjecture because $0$, the slope of a Seifert surface, is always among the boundary slopes. It is attributed in the paper to Ishikawa and Shimokawa; the supplied text does not indicate that it has been resolved.