Upper-degree conjecture for generators and relations of 3D space-group cohomology

Let $G$ be a 3D space group and consider its mod-2 cohomology ring $H^*(G,\mathbb{Z}_2)$. Upper-degree conjecture for generators and relations. An independent generator can appear at most in degree $6$, and an independent relation can appear at most in degree $12$. This conjecture would give a finite bound for computing presentations of the mod-2 cohomology rings of 3D space groups; the stated bounds are motivated by computations and by the structure of the Lyndon–Hochschild–Serre spectral sequence, but are not established in general.