B. Regression-preserving versus general complete-source changes

Regression-preserving changes are carried only by the new labels in ${\mathcal{V}}_{\mathrm{adm}}\setminus {\mathcal{V}}_{\mathrm{K}}$ (types $S\cdot {\partial }^{3}S$, $S\cdot {\partial }^{4}S$, $\partial S\cdot {\partial }^{2}S$, $\partial S\cdot {\partial }^{3}S$, ${\partial }^{2}S\cdot {\partial }^{2}S$, and the higher-degree parts of older types). General changes include the XVI-K ambiguity of XVI-K, Lemma lem:amb, as the ${\mathcal{V}}_{\mathrm{K}}$ block.