These are the fare basis codes, not the booking codes. So you're prohibiting fares called "N" and "K" and so forth, which actually don't exist, so the restriction doesn't do anything.

If you want to control booking classes, you want something more like "/f !bc=M&!bc=E..."

You can also use wildcarded fare basis codes; the industry uses a dash to indicate "any sequence of characters", and usually (but not always) the first letter of the fare basis corresponds to the booking code that will be used: "/f !ua..M-&!ua..E-&..."