Some errors from the crystallographic literature, some amplifications and a questionable result

Correction of space-group errors for some crystals leads to clarification of relationships among chemically similar but apparently crystallographically different crystal structures. There are new examples of the `centrosymmetric–non-centrosymmetric' ambiguity and also straightforward revisions of space groups. Finally, a questionable structure presents evidence either for a new type of N—H...Cl hydrogen bonding or for an error.