By the way, the triple negative is a sign that the "say what you DON'T want approach
" has maxed out on this regex.
At this stage, to refine the regex for readability, I might switch to a "say what you DO want
" approach: match (expression without "might contain") OR (expression with "might contain" in a way that is acceptable).
In the meantime, the expression as it is should work. Let me know if you need further help on it.
Technically, though, the expression above is quite interesting (for someone learning regex) because it showcases the use of a lookaround within a lookaround (specifically, a negative loobehind within a negative lookahead within a negative lookahead).