This is because there is a site setting within Luminate that dictates a 6 month window the event must fall in for it to show up on the list.

For example:
Today's date is 1/1/2015
An event is set to happen on 8/24/2015
This event will not show in the list.

The event must fall within a 6 month window (by default) to appear on the list of events that can be chosen.  In the example above, anything from 1/1/2015-6/1/2015 will work.

Contact support and reference this article and they can change the limits on the list to expand to more dates if required.