Hi, this looks to me as a very standard display, not related to the D+ version. One gets it using 'Function' key then 'Info' key which starts a rotating display.
Here it means: Info depth reached 5 plies, first move from the PV c7b7. Using the + key halts the rotating display, then +/- lets you browse next/previous moves from the PV.
This works using any version (B, C, D, D+). Also with Tandy 2150 which runs a B version.
I agree the manual is not that explicit about.
That is correct for D++, as far as I know. Yet the D+ was at least used in the Turbo King II. Maybe you meant the D+ was not offerred on the Corona and Michael's device has been upgraded later on?
MFG,
Eric