I am doing research on music history and I cannot find information between the four line chant staff and the grand staff. Also, I do believe that at different times in its development the staff actually had 12, 13, 14, and 15 lines. Where can I find proof or evidence of this?
I do not believe, except maybe in rare instances, that staffs that large were used. You may be thinking of Lute tabs.
All early music scores were written by hand. It's very time consuming to do this and they were after the most efficient use of space. This is why the 4 line staff with clefs and ligatures were used.
I would start, of course, start with Guido of Arezzo (inventor of staff, I went to his house once!). His treatise: https://en.wikipedia.org/wiki/Micrologus
A really great resource for notation, early music, and its evolution in a cultural and historical context is Richard Taruskin's "MUSIC FROM THE EARLIEST NOTATIONS TO THE SIXTEENTH CENTURY". I'm not a huge fan of his 20th century analysis, but as a former performer, scholar, and interpreter of early music, this one is hard to beat.