10.5cm case

[doppz92]

I found recently this German 10.5cm Feld Haubitze case, but unlike any other I've seen so far, this one isn't dated. The lot number, 120, dates it possibly from 1915, it's been reloaded 4 times and has the controller's mark Sp61, which is odd I think for Rheinmetall. Can someone shed some light on this mystery?

 

[Hoeksel]

Sp61 would be a marking for WW1 German army. Not sure if a case without year is uncommon, but I would think so. Most have a date. The Sp61 marking tells me it is not export.