Rational torsion generation conjecture for J_1(p)

Let $p$ be a prime, and let $J_1(p)$ be the Jacobian of the modular curve $X_1(p)$. A rational cusp difference is a divisor class represented by the difference of two rational cusps. Rational torsion generation conjecture. The rational torsion subgroup of $J_1(p)$ is generated by differences of rational cusps.

This is cited as Conjecture 6.2.2 of the referenced source and is used in the discussion of the case $\ell=2$ for $X_1(p)$; no resolution is given here.