Back in May, I won a really nice MSP lot at the Vogenbeck auction, but due to COVID, it's taken forever to get here. I finally received it today, so here's another show-and-tell.
Normally, mail sent from German naval vessels received the circular MSP cancel shown on the other items in this thread. On rare occasion, however, a piece of mail would sneak through without being canceled. Note, these were not situations where there was a damaged or lost canceller, leading to provisional remedies, but rather mere negligence by the postal clerks.
When this happened, the mail would be canceled using a handwritten notation upon arrival at the Marine-Postbureau in Berlin. These cancellations are known in German as Nachträgliche Entwertungen, or subsequent cancellations.

The text on the card I just received reads "Ungestempelt von der Marine-Schiffspost No. 6 a/B S.M.S. Arcona eingegangen/Marine Postbureau 30./3/98" (Uncanceled by Marine-Schiffspost No. 6 on-board S.M.S. Arcona / Navy Post Bureau / 30 March 1898).

The card was sent from the corvette-cruiser
S.M.S. Arcona in late-February/early-March 1898 while the
Arcona was participating in the German defense of Tsingtao, Kiautschou.
S.M.S. ArconaThe reverse has a photo of Barracouta Bay (present-day Sovetskaya Gavan, Russia) on 17 Aug 1897 pasted to it, and I'm currently having the text translated. I believe is describes a stop along the Russian coast while en route to Kiautschou.

As of the publication of Pohlmann and Kessing's
Handbuch und Katalog der deutschen Marine-Schiffspost und Marinepost 1895-1914 in 2009, ten of these MSP items with handwritten subsequent cancellations were known. Here are two of the others:


The use of handwritten subsequent cancellations stopped in early 1900, when the Berlin C1 postal cancel began being used instead.