Well, it did catch this one (at least, here) after the first few messages.
It makes sense there must be some limitations to how fast it can react
given the different ways these things get posted.
 
On Mon, 5 Jun 1995 00:36:49 EDT Ben Chi said:
>We've just installed 1.8b and it's failed its first anti-spam test.
>(And the Subject: line even said "ADVERTISEMENT"!-)  Have we failed to
>turn some feature on?