I drove one '99 I that had a very small key and the Infiniti logo wasn't painted. Then, I drove another '99 I30 that had a key similar to the G35. It had a piece of metal at the top and had a metal Infiniti logo. Does anyone know when the key design was changed?

 

A quick guess... it could have been a valet key.

 

infiniti keys made before 1999 did not have a decoder chip installed in them, 96-98 I30's did not have them, 99 I30's did. The 99 key has a chip in it with a rolling code which prevents for theft of the car, even if the key is duplicated the key wont start the car. Hope that answers your question