Scattered around are several threads, none very long about the 1917 Documentary Stamps and their their use on Parcel Post Mailing from 12-1-1917 through 12-31-1921. The tax rate was one cent per the first 25 cent in postage and once cent for each 25 cents or fraction thereafter. To be clear it was a tax on postage not on any additional fees paid with postage stamps (insured, C.O.D. and special delivery fees for example).
I have collected the threads here and note that they also show some War Tax usages as well as the documentary stamps:
https://goscf.com/t/83672https://goscf.com/t/78227 (This links to a third in the current last post)
https://goscf.com/t/87140 See post 3 specifically
https://goscf.com/t/85151 See 8th post specifically
The WWI Parcel Tax started December 1, 1917 and ended December 31, 1921. One cent per the first 25 cent in postage and once cent for each 25 cents or fraction thereafter.
Now that I got the organization handled above, I wanted to have a location to post examples of the WWI Parcel Tax when they are found, especially not by me but by other lucky collectors to have one or some.
I will start here and show a new find, well new for me after looking 42 years for these usages. I am posting two images, one is upside down so that a manuscript notation is easily read. I do not want to hide the fact that this was made by a collector.


Yes, collector inspired, but watch how the "stink of being philatelic" gives way to the invigorating fresh air of a tall pinnacle of a grand find.
This is a crossed center line block of Scott #C3. Based upon the manuscript note in the upper right above the block, it is clear the sender wants to preserve the block and willingly overpaid postage and fees. Here is how it can rate:
10 cents Special Delivery
25 cents Insurance (max at time, indemnity to $100.00)
47 cents Parcel Post Postage Zone 4 ( 7c 1st lb, 40 cent next 10 lbs, 10 x 4c/lb)
14 cent convenience over payment to secure used block
96 cents (4 x 24) in affixed postage.
Now the tax paid was 2 cents in Docs (Scott # R228, type 2, BEP printing), for PP postage over 25 cents up to and including 50 cents. Here, 47 cents was the maximum postage as one more pound pushed the tax to three cents, 51-75 cents postage.
What this shows is that a convenience overpayment of postage was NOT taxed for purposes of the parcel tax. This item collected the proper tax on just the postage amount affixed to pay the actual parcel post postage, not the fees nor the purposeful overpayment.
This is the first such PP WWI convenience overpayment taxed example, properly tax as well, that I have seen. I never expected to see one of these, only taking 42 years to find.
As a fun aside, I have several examples of C3 on parcels with war tax paid. C3 could be used as normal postage for non-airmail and non-SD.
Here the sender properly using manuscript, initialed and dated the documentary stamps to cancel them. Per rule, it was not the PO Clerk's job but the responsibility of the sender to manuscript cancel the war tax documentaries.
Now that said, I have seen them:
Manuscript canceled (with variations on initials and date)
PO Round dated
PO City only cancel
PO mute cancelled
Company round date revenue cancel
Company straight line cancel
Company cut cancel per a revenue document
Company punch cancelled per a revenue document
Uncancelled in any manner
Perhaps one or two others but none come to mind at the moment.
Normal stamps, normally postally cancelled for the tax
Normal stamps manuscript cancelled (initials and date)
Now can we see your examples?