Let $R$ be the ring of integers in a number field. While studying the congruence subgroup property for $\text{Sp}_{2g}(R)$ in

Bass, H.; Milnor, J.; Serre, J.-P. Solution of the congruence subgroup problem for SLn(n≥3) and Sp2n(n≥2). Inst. Hautes Études Sci. Publ. Math. No. 33 1967 59–137.

they quote a theorem of Bass that says the following. First, some notation. If $R$ is a commutative ring and $q$ is an ideal of $R$, then denote by $\text{Sp}_{2g}(R,q)$ the kernel of the map $$\text{Sp}_{2g}(R) \longrightarrow \text{Sp}_{2g}(R/q).$$ Also, denote by $\text{Ep}_{2g}(R,q)$ the normal subgroup of $\text{Sp}_{2g}(R)$ generated by the usual elementary symplectic matrices which happen to lie in $\text{Sp}_{2g}(R,q)$.

**Theorem** : For $R$ a Dedekind domain and $q$ an ideal of $R$ and $g \geq 2$, we have $\text{Sp}_{2g}(R,q) = \text{Sp}_{2}(R,q) \cdot \text{Ep}_{2g}(R,q)$.

This is part a of Proposition 13.2 in the above paper. The reference they give is

Bass, H, Symplectic modules and groups, in preparation.

However, this paper does not seem to have ever appeared. In a paper I'm writing right now, I need a fact which is a corollary of what I assume is the proof they have in mind (alas, it doesn't just follow from the statement). Does anyone know a published account of it?