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Steve,

It all depends on how much you want to spend on your chart plotter.  ECDIS grade chart plotters will maintain a DR plot based on heading input (compass) and log (typically sonar) if GNSS inputs are lost (the alarm alerting you of this makes an racket).  They also allow manual inputs of range and bearings from objects and will plot a fix based on the input data.  There are even tethered devices that allow you to target a NAVAID, push a button, and the LOP will be plotted on your chart automatically.  I even worked out a way to add Celestial LOP's, but that's another story.

You can also use radar overlays to "correct" the chart display.

So while GNSS input is certainly the primary input, and usually there are several; more advanced chartplotter systems allow for the alternative fix procedures you discussed

Jeremy