I don't think they have.  I only know that experts consider them to be somewhere between 300-400 years old based on when the Ojibwe have lived in the area.  Also, lichen that has grown over pictographs has a known rate of growth and that has been used to date them. Schoolcraft (1850) noted some in his explorations and drew them.  Other explorers asked their guides "who did these?" and they said they didn't know.  I also heard that the Montgomery Creek pictographs may be older (from Park personnel).  Bob Evans and Edwind Trout have researched all the pictos and have been publishing "Bulletins" so that people can find them easier.  They include lots of interesting facts in the brochures also.  I went with them to Swartman lake.  We bushwhacked there a few years ago.  People have come out of the woods literally to tell the of sights that are not known about.  There are some interesting stories to tell about these new pictographs and hopefully they will share them with everyone sometime. Happy pictograph hunting.  Kim