Common Lisp wasn't standardised until 1994.
Also, SBCL has some nice features specific to them, I'm sure it's the same for other implementations. So while there's a lot that's common between them all I find myself using a lot of platform specific functions.
Yes, but it existed before then (from 1984 on), and a large amount of code written for CL pre-standardization still runs without alteration or with minimal updates.