We should dedicate a little space here for what’s known as the anonymous personality or entity.
By that we mean a manifestation which is obviously a human being, but who is unknown to the observer(s) or who eludes attempts to be identified through historical research.
Simply because the entity can’t be identified however, doesn’t mean they don’t have a logical fit at the location contextually.
Soldiers who appear on or near battlefields are a good example. These entities are clearly human spirits and the reason for their appearing at the particular location makes complete sense, however their specific identity is and will probably remain unknown. In those cases the entity is likely to stay anonymous because of the sheer number of fatalities at that location, none of whom lived there and most of whom had no historically recorded presence.
The best example of this phenomenon is far and away the battle sites at Gettysburg.
But there are as many reasons as there may be cases. An anonymous entity may simply have been visiting the location or there may be more sinister reasons for their presence.
As far as investigation in concerned, this type of entity can be problematic.
In the case of familials there is generally a reason for their presence and that reason almost always involves communication with the living. Similarly, historicals usually feel as though they belong at their location and as a result are often more than willing to communicate.
Those entities that remain anonymous however frequently appear to be angry, frightened or confused. They may not understand where they are or why, so they may be more frightened of the living than the living are of them and that fear makes them reluctant to interact.