There are generally a few strums or picking patterns that are used in any given folk style--(and often, it is really just one) with some common embellishments and variations that are applied at the discretion of the player--but as long as the player keeps the feel, they can bring nearly anything else into the tune--

Some things that people play on the guitar are hard to notate because it is relatively easy to play a complex rhythm, then, with a few strategic finger maneuvers, create a bass line that moving in a different direction---you've got four voices going one way, and one voice playing something else, so you'd need to write out a conductor's score to show what's going on-