- Published court decisions;
- Court rules;
- Legislative acts, or statutes, and;
- Administrative regulations.
The first item on the list, published court decisions, is the exception.
A published court decision does not change once it is published. Later court decisions can change the meaning or the validity of the earlier decision, but they don't go back to the first decision to add a footnote letting you know that it has been changed. They do not do that. It is one possible reason why some lawyers sometimes drink too much. It is a constant worry that they missed out on an important change.
The main trick for researching court decisions is to work backwards in time, and start with the newest decision first. Older cases are still sometimes very useful, but more skepticism and research is needed.
Court rules, legislative acts and administrative regulations are a little easier, in this respect: They are updated and supplemented regularly and each rule or statute generally has a revision history. This is an example from the Kentucky Rules of Civil Procedure, CR 11 Signing of pleadings motions, and other papers; sanctions:
This rule was first adopted by the Kentucky Supreme Court in 1953 but amended in 1963 and 1989. If you are reading a Kentucky Appellate Court decision from 1959 discussing this CR 11, you know it is a somewhat different rule they are talking about and there is no point looking for case law before 1953.