The 1925 listing is not for him, it's for his wife. If you look at the scans of the directory (not the transcribed index) he's NOT listed -- something like "Decker Mary wid[ow] of Luther H" is. I'm trying to determine if he ever lived there or whether only his wife (and possibly son did.)

Have you been able to find a listing for him, not his wife, at that address? If not, what is his last known location?

A listing for his widow is not a listing for him. She could have lived any where after his death.

Finding his last known location is necessary for finding a possible death location and year, and then a death record.