Here is my 3cents worth. The nice gun shown was likely re-built in the 90s from a plainer gun made in 1929 and proofed in the Zella-Mehlis Proof house. While seemingly unusual, it is possible the gun came from one of the Suhl makers, unfinished , then finished and submitted to the proof house by someone in or around Zella-Mehlis. It was, and is, common for manufacturers to sell, to "the trade", guns in various stages of completion to others for final completion. Much later, it was likely re-stocked, re-chambered, profusely engraved, re-finished, and submitted to either the Munich Proof House or Munich's sub-facility in Mellrichstadt(?) for a new proof. The horn triggerguard could have been original, or added in the re-work. As far as the engraver being drunk when he stippled the background; it could be possible, but there is no way to know now. The most likely explanation for the mistakes is the background was not likely done by the engraver, himself. Such background work was, and is, usually done by less experienced persons training to be engravers. It could have been anyone, even the 15 year old daughter of the engraver; the identity is not known now. The gun should be accepted for what it is now, a fine gun, and what it used to be is no longer important.
Mike