In peacetime, the German Army was uncompromising with regulations. From mobilization onwards, anything goes - it's called Ersatz, and it's camouflaged by the headgear. Fortunately, we have some extraordinary photos to show us these “imperfections” or liberties in relation to the regulations.

The Strelitz tip should be standard (Prussian). However, this point is a genuine Schwerin (M97/15), not a Bavarian M86/15 (see my comparison above).
Infra : It's not a photo, but it's a KR M15 with a hint of JzPf. Under the CC, invisible.
Infra :This reservist from the 2 or 3BRIR109 still shows us an M1887 helmet that has been reformed, but reactivated on mobilization. The Perlring
tip is still there, but the side-post chinstrap has been added and metal visor trim ring.
Here's a photo of an M95 to M15 helmet recycling workshop. Crest button, with 9 holes instead of 5.
