Spooky, you're talking semantics here. My (basic) Litton 92 notes tell me that the IRS position can be updated by an external source. In the fit I was referring to, this souce was the FMS900 which excluded the radio nav aids if the GPS source was accurate. Threfore as far as I'm concerned, the IRS is being updated by the GPS. And as far the EGI is concerned, it's a combined position. An IRS position enhaced by GPS or a GPS position stabilised by the IRS? I don't know. But it did receive the encrypted Y channel GPS signals, so it was in a different league to the fit on airliners.