Those ratings don't mean a thing to the American Library Association.
At my public library, there are restrictions on what children can check out (e.g. no rated R movies) and parents are given the right to put further restrictions on the card as well. Accessing pornography is strictly forbidden. Those librarians get pretty livid if someone tries to.
The ALA's position as posted on their website is that there is no such thing as "age appropriate" material. They believe that if it is in the library, all patrons should be able to access it.
This doesn't mean to them avoiding stocking something like Madonna's Sex book or an "X" rated film like Last Tango In Paris, instead it means requiring parents to restrict their kids card (since by default the ability is there) so that they cannot check out ANY videos without parental approval. Not sure how the library wants books "limited" in access since no arbiter reviews books. There is a "code" for comics, but the x-rated works of Robert Crumb (which do have some valid content) carry no CCA code.