There have been a good number of changes over the years but for the most part they’re the sort of thing that will just prevent an old extension from compiling rather than introducing a subtle shift in functionality.
I’m going to tag @Zed since he’s done the yeoman’s work of testing all the extensions to see which are current and which throw off errors, as well as making some tweaks to update them when possible; see thread here and results here. Hope this is helpful!
EDIT: Sorry, I answered this while half-asleep (had a sick baby sleeping on me) – looks like you do want to know the details of the changes. There’s a comprehensive writeup in the documentation so it’s certainly possible to work through that; the organization makes it pretty easy to skim the headings and see roughly what the changes were… until you get to the “earlier builds” section and realize there’s a lot of content there, too, and it’s all basically just in long text files.
Overall my sense is that if you’re a beginner looking for examples to help you understand the language, you’re very likely to go too far astray; there are some new added features, like responses, that you might not see used in earlier sample code, and there are some lower-level changes that will make wholesale copying-and-pasting challenging (this is where the extension stuff I linked above will be helpful). But if you write your own code following the examples you’re seeing, and compile frequently to test whether there’s some weird issue that seems to be breaking things, I think you should mostly be fine.