It is a bit hard to help when we dont know exactly what lines you have already followed without success, no point in going over old ground.
Who were Victors parents? What siblings did each of them have? Did any of these (Victors aunts and uncles) marry a Coe? What children did each of these siblings have? (ie Victors cousins) and did any of the girl cousins marry a Coe? Once all those lines have been explored fully, then you need to think further afield - have you reached that point? Next step will be to look at all four granparents and go through the same process.
I see this was in WW1 era. Have you looked at 1911 census and seen what Coes are around in Cornwall then , just a few years earlier? (Sorry look ups not allowed)
