More or less in consonance with @John K, here, step by step, is what happens on the later jets:
This is describing the VNAV mode behavior when crossing the "FI" ie the FAF, Final Approach Fix, waypoint, ie the GS intercept point.
The scenario would be that an ILS approach is selected via DEP/ARR page (i.e. from database), and there is a VNAV PATH from the FAF descending to and terminating at ~50ft above the LDG threshold.
If you're shooting an ILS, you're tracking the LOCaliser and the vertical mode is VNAV ALT or VNAV PTH and you're approaching the FAF (depicted as FI).
(Case 1) LOC has been captured GS is armed, the VNAV will disconnect and GS will be captured and become the active mode.
If GS is not armed,
(Case 2a) If the altitude window on the MCP is set to MDA, the airplane will continue on VNAV PTH and commence the descent from the FAF to the MDA.
(Case 2b) If the altitude is set to the FAF altitude or higher in the MCP window, the mode after crossing the FAF will be VNAV ALT.
Thus, in either case of altitude setting, if GS is not armed the VNAV will not disconnect crossing the FI (FI = FAF = GS intercept point)