Restrictions that set binary variable to 1 when integer variable equals x, 0 otherwise
In this case (where the possible sets of values are finite) a graphical approach can work nicely for determining a suitable set of constraints. Draw the points in the set $\{1,\dots,12\}\times\{0,1\}$ in the plane, using $+$ for allowed and $-$ for disallowed combinations:

$\begin{array} &amp; &amp; + &amp; - &amp; - &amp; - &amp; - &amp; - &amp; - &amp; - &amp; - &amp; - &amp; - &amp; - \\
 &amp; - &amp; + &amp; + &amp; + &amp; + &amp; + &amp; + &amp; + &amp; + &amp; + &amp; + &amp; +\end{array}$

Can you find a set of lines separating the $+$s from the $-$s? Note that $Y+MONTH\ge 2$ already take care of the $-$ in the bottom left corner.