Aircraft fitted with IRS don't have IVSI's - because you don't need an Inertial Vertical Speed Indicator when you have an inertial platform (the IRS) already fitted.
Dunno, the VSI in our 733s was called an IVSI, however the airplane was of course fitted with two IRS (strap down, not a platform of course).
Since retirement, I’m not even allowed in an airline cockpit, but perhaps a current pilot will confirm that, by the end of a long flight, the GS readings on the captain’s and F/O’s displays typically differ by several knots
Afraid not, it will always read 0, nothing else. On our 737 classics it sometimes had 1 or 2 kts difference after a 12 hour day, on our NGs not anymore, no matter how long the flight.
On the 737 the FPV on airplanes without HUD is purely additional information, its use is not required by any kind of procedure or approach. NPAs are flown in approach mode following the exact same presentation as on an ILS or GLS approach.
By the way, how does Boeing word its warnings?
There is no warning in our checklists. In fact there is the following info in the IAS disagree checklist. Nothing at all in the ALT or AoA disagree checklists (AoA disagree leads to IAS and ALT disagree).
Additional Information
The flight path vector is based on inertial sources and may be used as a reference in maintaining proper path control.