There's all sorts of 'explanations' for details of construction - but they certainly aren't rules. Almost all the variations can produce a good-sounding guitar in the hands of a skilled builder.

I have an old standard-sized, flat top Italian guitar by Alfredo Albertini, who was better known for his mandolins. As you might expect, it has a tailpiece and a movable bridge. I've strung it with both steel and nylon strings over the years and it produces a bright but mellow sound with either.

Phil