If you mean that pronunciation of family names is a reliable guide to how the word was pronounced, I would want to check that with all the Deaths and Deadmans around here first.

Pronounced, on the most part, as Deeths and Deedmans, no doubt? Wonder what one had to be up to in antiquity to be dubbed with such a monicker? And why would one allow such a name to stick? 

   "You're a deadman!"

   "Cool! I kinda like that name! You can keep calling me that if you like...
uh, instead of killin' me."