Conditional placeholders don’t work because they invoke some function which produces some output but they don’t contain the output themselves. Eventually I stayed awake for most of the night and solved the problem ?? For the record, I found that it is possible to do something like this:
[Start example]
global $post;
$EM_Event = em_get_event($post->ID, ‘post_id’);
$nmonth = date(‘m’,$EM_Event->start);
[End example]
In this example what I’m getting is the date of the event for the current event being displayed. This is (third line) formatted so that $nmonth will contain the numerical identifier of the month (January=1, February=2, etc.). With this variable I can solve my problem. I guess this is pretty basic but may help somebody else.