I've filled out my MCA with the State Bar of California.  On it I disclosed an arrest that led to a no contest plea with an ultimate dismissal (deferred adjudication, no conviction).  This is consistent with what I reported for three other state bars that I am now admitted to.

The problem is that I don't think I reported this to my law school (more than 18 years ago).  If I recall, the application required me to list all arrests.

What's the likelihood that the State Bar of CA is going to pull up my LS app and call me out for not reporting an arrest that never led to a conviction?

FWIW, there's nothing else of interest on my MCA.

I don't think that will be a problem. Just be as honest as you can, and if you have ANY question as to how honest you should be, contact a professional lawyer who represents people before the state bar. It is always good to have solid legal footing before answering those painful questions. A good 200-300 bucks on one can save you a lot of money.