Keep trying for that death certificate, but keep in mind although TX officially began keeping vital records in 1903, not all counties got on board until later. Also, since he died in 1917, about the time of the great influenza epidemic, his death might not have gotten recorded. I have an ancestor who died in 1918 in NE, I have a photo of his headstone and a copy of his obit, but there isn't a DC at the county or the state level for him.
I have a copy of a copy of a DC for an ancestor who died in TX in 1926. It was sent to me by a distant relative. It's not very clear and it's white on black to boot. So when I was in Uvalde Co, TX I went to the courthouse thinking I'd get a fresh clear copy so I could read the name of the funeral home. They did not have a DC for him there in the courthouse. The lady was very helpful and really looked through their records, and it was then we noticed my copy was from the state, not the county. I can't figure out how the state got the record if the county didn't notify them.