A franchise document from 2014 (you'll be able to find it on the internet) says two HGI's were company owned in 2013 (out of 500 in N-A).

Hilton Garden Inn El Segundo, CA, next to LAX, is most likely one of them, because it's not on the list of franchises - active on December 31, 2013. This property helped develop the HGI and other Hilton brand standards. I wouldn't know which HGI is the other, it probably opened somewhere around 1996-98 East of the Mississippi, I would guess.

I don't stay at HGI that often, but have received multiple junior suite upgrades across the US, though never an upgrade to an experimental suite at the HGI El Segundo.