The newest version of the MLA manual came out in April and so the OWL Perdue website is technically out of date. Also, additional websites (including the Illinois State University page on citing government documents) all differ quite extensively when it comes to requirements of citing US Government documents and what information you should include. I am reluctant to buy the new edition because even the official manuals are confusing concerning specifics of this detail.
That being said, I want to cite this document https://www.gpo.gov/fdsys/pkg/PLAW-107publ40/pdf/PLAW-107publ40.pdf (as is, in the online version) specifically. I am unsure whether it is important to note that it says "Congressional Record" on it, which was mentioned in various university website guidelines, something along the lines of "If another agency published it, you may not need to include GPO in your citations." Also, how would I find out whether it was in print before it was published online? How would I note that it is an electronic reprint if it is? What does S.J. Session 23 mean, and is it necessary to include this info in the citation?