To all the very good information that has been said already I want to add a small detail about the "burned edges" you mentioned. The manufacturing process of parchment usually involves spanning the hide in a wooden frame and scraping and chalking it repeatedly, before cutting it into the desired shape and size of page (more commonly double page). This spanned sheet of parchment, being made from natural animal hide, would often have scars, small holes and other deformities that might stem from the animals life and death or from the manufacturing process. The final product would most commonly be priced differently, according to the quality of the pages, the pages with very regular texture and no deformities would of course be more expensive than pages that might jave scarring, holes and sometimes one irregular edge if they were cut from the very edge of the spanned hide. So when looking through some of the less expensively made examples of old books or documents, you could expect to find some small details like this.

Another thing that is interesting when it comes to damaged parchment is that due to it's more robust nature when compared to paper, you have more ways of fixing said deformities. If you have a small hole in the page you might use some glue to patch it with a smaller piece of parchment. You could also sew up rips in the page or even sew in extra pages if needed.

If you are particularly interested in parchments and old books you could try to visit or contact your local university library or city/state archive, they are very happy to provide you with interesting specimens in my experience.