Rookie officials have recently spent a lot of time with their heads buried in rulebooks, and casebooks, to prepare for the rookie exam. They are only required to know (with the exception of the "new" team control on a throwin backcourt rule) the most recent set of rules. A difficult, but not impossible task, and some do it quite well.
Veteran officials have been through years, and years, of rule changes, and casebook interpretation changes. Dozens of changes for most. Hundreds of changes for a few. Sometimes these changes can be just as confusing, or more confusing, than the original rules that they learned many, many, years ago.
I had a brand new official straighten me out with the "new" kicked ball on a throwin interpretation a few years ago during a freshman game. He was so new that he still had that new official smell. My response to him, "Thanks partner, nice job."