When you constrain a start date, to exclude older imagery, for an area if no more recent imagery is available, is a blank layer returned or your default, low-res (old) satellite imagery? It would be very useful to see that there is no recent imagery after the constrained end date.
You simply get no layers if you create an area with a polygon and restrict the dates to a particular range. The satellite layer, which was by default included in our last version of WMS, is no longer included in the responses, so you do not get satellite imagery unless you explicitly ask for it. So yes, it would be possible to see that there is no recent imagery after the constrained end date.