Do you need to answer yes to have you ever been "declared incompetent" if you have been involuntarily commited to a mental health facility but the records have been expunged. I have been advised by my attorney that I am legally allowed to answer no to this on all forms because it is about mental health. He said that I would need to divulge expunged criminal records but never would have to divulge expunged mental health records.
I would advise being totally up front and honest on the form, regardless of your attorney's advice. There is nothing on the SF-86 for this question that says you do not have to list it if your medical record has been expunged.The question asks "have you EVER". Seems pretty clear to me, read the question and caveats of what situations you don;t have to answer "yes" and go from there.
Look at it this way: if you voluntarily disclose this, more than likely any concerns can be mitigated, particularly with the passage of time and no further incidents. But if you do not disclose it, you are basically gambling that it will not be discovered, because if you do not disclose it and the investigation uncovers it, then you not only have to mitigate the incident itself but also the fact that you attempted to conceal it.