I normally have my symbology set up so that it only shows one icon for all similar features. For example, I would have one symbol for all firestations, etc. However I do break up unique items like policies or criminal events, etc.
One of the primary functions of the Dynamic Legend is to allow the layers to be removed from the legend as they disappear within the map view, usually due to min/max scales.
A quick test indicates that in its default mode, while the individual layers come and go, the various icons in a unique layer are always present when the layer itself is present. So in other words, depending upon how you set up your original map it may or may not work as you hoped...
The best person to ask regarding the Dynamic Legend is Rob Scheitlin, the author. It may or may not have additional settings that would let you do what you want to do. If you create a new thread discussing the Dynamic Legend directly with his name in the title, then he will usually get in touch.
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