For the record, most manufacturers out there are not going to specify a specific date in which their meal expires. But, as noted, freeze-dried meals can remain edible for several years (often a few decades). With that said, you may encounter a situation where your backpacking meal has expired.
At this point, it does not technically mean that you have to throw it away. But, after it has expired, there is no guarantee that it is not going to spoil and lose most of its nutritional value.