The completeness conjecture for morphisms between degenerate Verma modules over E(5,10)

Let $E(5,10)$ be the exceptional Lie superalgebra, and consider its degenerate (minimal) Verma modules. The source constructs morphisms of degrees $2$, $3$, and $5$ in addition to those of degrees $1$ and $4$, namely the morphisms listed in Propositions 2, 3, and 5 and Theorems 4.2 and 4. The completeness conjecture. These listed morphisms are all morphisms between degenerate (minimal) Verma modules for $E(5,10)$; in particular, there are no morphisms of degrees larger than $5$. The claim would give a complete description of morphisms among the degenerate Verma modules, but the supplied text provides no proof or resolution of it.