Hi pacifistas,
If you reset and reprocess your notes it should solve your strange sample sizes. I think this happens sometimes when updating from a very old version of NoteCaddy to a new version without resetting the notes.
How to reset NoteCaddy notes - Assaultware Wiki.
Regarding your 2nd question, I don't believe it's possible, unless you construct the definition differently by selecting "Do not take notes for missed opportunities". That will make the definition not show a frequency % any longer though.