Delphi Class variable per class

You are missing nothing. Your analysis of how class variables work is correct. A class var is nothing more than a global variable that is scoped by the class.

One simple solution for you is to use a dictionary to count the instances. A more hacky approach is to use a trick of mine that Hallvard Vassbotn blogged about, which (ab)uses the VMT to store class-specific fields. You can read all about it here.