Like Agur, I find some things are beyond my ken.  It is, for example, beyond my understanding why the Securities and Exchange Commission thought it would be a good idea to use three different measures of time in Rule 144.   

Rule 144(b)(1) refers to the "preceding three months" while Rule 144(b)(2) refers to "90 days immediately before".  Does this simply reflect the SEC's preternatural predilection for "elegance of variation" or did the SEC intend different meanings?  The rule is further clouded by the ambiguity of the term "month".  Is the SEC referring to the preceding three calendar months or the numerically corresponding date in the third preceding month?  Rule 144(e) further muddies the water by referring to "four calendar weeks preceding".