Custom properties created in Presentation Parameters do not need to be used in the task subject or description.
To view a list of the properties you create, deploy your process to the server, display the Process Console Catalog page, and select Task Properties
Property names do not need to be unique, if added as different types. For example, you can create a property named "priority", once as a string and once as an integer. The Task Properties list appends the type to the name:
Allowed types are string, integer, double, boolean, date and dateTime.
You may want to take advantage of the Process Developer custom function getOutput as an expression for a property. This allows you to filter a task list using an output message part.
Task properties deployed in the .avcconfig file are not tied to a particular process. They are for general use in a task client.