Turn out this is just my misunderstanding of what the "Stiffener #1" column is supposed to show. That column only shows the stiffener that is applied to the duct _if_ only the duct needs any stiffener. Even if the edit-duct screen shows that it needs a stiffener during the course of editing the properties of the duct, CAMduct seems to do a last minute check when it saves the duct and may decide that the duct doesn't need any stiffener after all. That results with the edit-duct screen shows that a duct needs a stiffener, but the Item Folder shows no stiffener for the same duct.
This simply means that this is a case of wrong expectation in my part. I am glad that this is no longer a problem. Thanks for all the posts that have pointed out the free trial doesn't have any limitation, and I just need to keep trying to figure this out.
Jaysom