The spelling you mentioned on the tombstone is what I have been told by many German speaking Americans is the phonetic pronoucation of Jacoby. That is what an English speaking clerk or funeral director or stone carver would hear if Jacoby is spoken by a German speaking person. I have found it several times out of the blue when following my Jacoby family. I've worked with someone doing Jachowski, and he has the same situation. The "J" sounds like "Y". Hope this helps.