Hi there,
I still cant find a death record of him

I did find the list of names that were killed and as you said 8 names and 2 unidentified. Im assume that your fella maybe one of the unknown as he isnt any of the 8 that were named.
There are some things that confuse me. Why no death record [that i can find anyway] and why if the family knew it was him that died that his name isnt on the list of the dead and or why there is no death record as one would think they would have registered his death? If that is him on the family tomb as dying Oct 1917 maybe see if the burial record for that plot might tell you something.
All very mysterious, comfusing and intruiguing.