Look at this screenshot below:
I am an ex-googler and seems that when i was using this phone (Google Nexus Prime, i9250 or Nexus3 as they say) I was using internal (Google internal) upgrades. But probably I left the company while I was having an interim build and since then could not move to latest ICS or JB.
Hope fully you got the issue. Could you please guide me on how could I get to the latest android without hassles? (my current build IMM76B is probably not known outside Google)