How can I SELECT an 'entry' that spans adjacent months?
I keep the following bit of ASCII art around that I drew a few years back as reference for dealing with matching ranges, reformatted, as it was originally in POD; in your case, you're using the second one, which only matches example 3:

Interval Matching

 .........A============B......... Search Range
 ...x--y..|............|......... (never match)
 .........|............|...x--y.. (never match)
 ......x--|--y.........|......... (1)
 ......x--|------------|---y..... (2)
 .........|...x-----y..|......... (3)
 .........|..........x-|----y.... (4)



Intersection ... matches examples 1,2,3,4

A &lt;= y &amp;&amp; B >= x
(item fully contained by search range) ... matches example 3 only.

A &lt;= x &amp;&amp; B >= y
(item fully includes search range) ... matches example 2 only.

A >= x &amp;&amp; B &lt;= y