Not sure if it helps but we had a similar issue with drop downs (rather than list box) with dates.
We ended up creating an extra column in data prep where newest date was shown as 'latest' rather than the actual date (we made it a text field), we then selected that in the report and saved so that 'latest' was always the default selected option
I recommend using the slider (I run VA in swedish, so I'm not sure it's called "slider"). It can be used for picking a range of dates or a single date. You can make it default to the maximum value (most recent date) in data.
It includes a descent date-picker, so you actually don't have to use the slider-tool. That helps a lot when you have a long time-range to choose from.
See how to use one filter for multiple data sources by mapping your data from SAS’ Alexandria McCall.
Find more tutorials on the SAS Users YouTube channel.