As I have just written in another comment: But they were already wrong in the cited source and we had the original documents to proof that. He just wasn't will

As I have just written in another comment: But they were already wrong in the cited source and we had the original documents to proof that. He just wasn't willing to look at them. To add to that - the source is a digitized out of print book that will probably never have another edition or printing. I could start a website or create a blog post with parts of the proof documents and maybe even sound snippets from an old interview (and part of old Stasi documents as well to make the point and that to be referenced by Wikipedia as a new source. But why would I need to go to these lengths if I could provide proof to Wikipedia more easily if they wanted and have them at least remove the wrong parts. Even if they would not include the corrected things.