Resolution:
TRA Scripting Deployment User's Guide (Chapter 2. Getting Started, Other Options) states:

<<<<<<
-truncate Option
    With this option you can remove unwanted revisions of an application by specifying with this option the number of the most recent revisions to keep. ......  The following example truncates the application's revision history to five revisions.
    AppManage -truncate 5 -app timer_wait -domain tp001 -user admin -pw admin
>>>>>>

This is incorrect. "-truncate" option does not take a value, instead it truncates the application history to the number specified in Max Deployment Revision of the application.