Not Sure How This Postage Due Adds Up On This Cover.

Did they apply too much? it shows 8 cents due and 12 cents was applied.
It also looks like it was used for official business. So why the postage due?

Looks like the circular part of cancel does not cover/tie stamps to cover, maybe the stamps were added later??

edit for clarity

Yes they were because of postage due. but I think too much was added.

May be something as simple as having those stamps handy and not willing to take the time to look for the correct amount?

that is what I am thinking! but want to make sure I didn't miss something. Since these stamps I assume we added back at the post office. but again why was postage due needed?

Was the Via Airmail added before or after the stamps? If before, would specifying that have made a difference causing the postage due?

First impression:
Penalty mail is for surface transmission only.
They marked it "via air mail" and mailed it without any postage anyway.
Postmarked on ship and sent on.
It got returned for the proper airmail postage.
Sender didn't have an 8 cent airmail stamp and slapped two 6's on it (partially over the previous ship postmark) and reposted it.
Stamps then got canceled by the killer portion and sent on the the destination.

so even though used for official business, sending it air mail requires postage? Thanks for the info!

Generally, yes. There were exceptions for the USPOD and certain military origination urgent sendings with permit mail. A special endorsement was needed.

Here are two examples:






There are others.

Veery nice! Thanks!