Links to any page can include a promo code or source. When a link containing a promo code or source is used, the source is entered for the session.
To embed a promo code or source build your link like this: http://tickets.sampletheatre.org/default.aspx?promo=<promo code or source number>
Promo codes can be included with any of the other parameters listed in this topic. For example: http://tickets.sampletheatre.org/default.aspx?promo=ailey&m=1&y=2012
Your syntax should be correct, however, the url
https://support.arvadacenter.org/?m=12&y=2013
Does not change your calendar either, so looks like it is how the calendar is coded that is causing the problem.
A member of our consortium uses TNEW and you can see that the following url direct you to the correct month on their site.
http://ticketing.greenwichtheatre.org.uk/?m=12&y=2013
Mark