In the bookcases of many TV Libraries I have often seen there being sets and volumes of recognizable law reports and journals even in situations where they should not have them. I have seen recognizable AmJur, Corpus Juris, the All England Reports etc etc.
Why do props departments use them. It cannot be the cost, as many of these reports and journals are quite expensive.
Are out of date ones expensive?
Law Reporters are usually published by year, for example All England Reports 1922, All England Reports 1923 and so on. Generally you will ask for the complete set and get a new one every year. So, yes quite expensive.
Sometimes they aren’t real books. The prop department just slaps up the standard “educated bookshelf” prop and lets it go.
But the ones you see on tv sets are likely not this year’s or even last year’s. They are almost certainly bought bulk secondhand.
As to why they are used, it is simple shorthand for legal setting. People are used to see books that look like those in news shots of court rooms or lawyer’s offices, and they equate that look with a legal setting. There are plenty of the old reporters and journals available and so props departments can pick them up cheap. I clerked at a firm that was getting rid of its library for office space and their books almost certainly went this route. The books had not been updated in years and were for show.
Because they look lawyery, and 98% of the TV-watching public doesn’t know the difference.
^
My point is that I have seen them in settings where you would not expect to see them, a School Library, a hospital office, a City Hall.
Doesn’t matter. The set decorator calls for “an impressive shelf of books” and the prop department delivers. Nobody cares if the books belong in such a place. All they have to do is look impressive and take up shelf space. It’s not like it’s important, like using an 1873 Colt in a Civil War drama. 
My favorite use of that adjective ever was
[Fred Gwynne in My Cousin Vinny]And the next time you come into my courtroom you will look lawyery… I mean you will comb your hair and wear a suit and tie, and that suit had better be made out of some kind of cloth![/Fred Gwynne]
As mentioned, these journals are very expensive, and usually the lawyers and clerical staff use WestLaw and or Lexis because they’re easier and more efficient. However, many if not most law firms do still get the print (there’s no ‘per minute’ access charge on the print). I think the real reason though is because they do look lawyerly (probably the same reason some firms keep them around) and you have to convey where you are without using precious screentime.
Many movies and TV shows will also show doctors wearing white coat/scrubs/stethoscope even if they’re in their office or having lunch in the hospital cafeteria or otherwise not coming straight from an examination but in a place where many doctors just wear street clothes; it just gives an instant visual I.D… College professors, even if they’re tenured and respected names in their field, usually have offices the size of a walk in closet, but in movies/TV they often have large old woodlined offices because this conveys ‘fancy shmancy intellectual’.
It makes me wonder about courtrooms, too–real courtrooms. I’ve been to at least one where there was a shelf of law tomes behind the judge, but really? When is the judge going to say, “Hey, let me just look up 'The People vs. Jones from 1954, to see what to do here…”
Could those also be fakes?
Out of date reference books are both dirt cheap and pretty impressive looking. Another favorite seet dressing is Reader’s Digest Condensed Books. They came out about four times a year and the leather covers came in different colors so you could mix or match them on the bookshelf as needed.