Yes no relation with the fight of JR 117 in 1914. In the case of a wounded soldier sent in a Feldlazarett, there is no reason to see such a writing, as the soldier here didn't become prisonner after.
A exceptionnal set pickelhaube/Uberzug ! As OJR 91 raised I/RJR 74, there is a logical connection between the two units. I would say a lack of plates which needs to take what was avalaible. The stores asked help and received what was available.
Generally, such prices appear when two auctioners really want the item. If such another shoulder straps is offered in auction, I guess the final price would be lower.