Any school with multiple entry dates for a graduating class may wish to filter for constituents who joined the school in a given year, rather than by their leaving year. For example, we have just digitised our admissions records for pupils who joined the school 80 years ago, and would like to contact those who are still alive to let them know that they can now view their admissions records online. Those pupils all joined in 1941, but might have been members of any Class of from 1943 to 1950 depending on their age when they enrolled - and some of those would have left the school before Sixth Form, or even stayed on after their scheduled departure date - so Class of is not useful in this scenario.
We can make a query in the database, but these fields are not available for selection in the list builder in NXT, and most of our team use NXT for the majority of their RE work; it would help them (and save them from asking me!) to be able to build such lists themselves.