Hi, your rules looks like ok. You can try search for these registry key to see if they exists :
<sdp:IsInstallable>
<lar:And>
<bar:RegSzToVersion RegType32="true" Data="18.0.0.209" Comparison="LessThan" Value="Version" Subkey="Software\Macromedia\FlashPlayerPlugin" Key="HKEY_LOCAL_MACHINE"/>
<bar:RegKeyExists RegType32="true" Subkey="Software\Macromedia\FlashPlayerPlugin" Key="HKEY_LOCAL_MACHINE"/>
</lar:And>
</sdp:IsInstallable>
Also, you can edit the update and look at the metadata of the MSI file. There is some "IsInstallable" rules in it.