Occasionally the ducks or stars line up and one can accomplish something. This thread is one such occurrence.
Here is a great thread on Canal Zone stamps and a tiny bit of postal history:
https://goscf.com/t/7629&whichpage=1 but I did not want to suddenly add a group of specialized Canal Zone postal history. So this thread was created.
On pages 3 and 8 of the link above was shown this cover:

This solo usage of the Canal Zone overprinted US Scott 803 (Scott Canal Zone 118) is a difficult to find usage and merits a Scott listing for being on cover in this manner, single usage on 1 cent PSE envelope paying third class. Most serious Prexie collectors also collect this overprinted Prexie stamp along with Canal Zone 119 which is the 1.5 cent Scott US 805 with the Canal Zone overprint. It, the 118, is not a cover that most Prexie dealer have in stock all the time. In fact at least one Prexie dealer has never handled one. When one arrives in stock, it does not stay in stock long.
That said, one seller on
ebay listed nine covers at the same time a couple of weeks back. Each as a buy it now listing. All are shown below. Under each set of pictures for one cover I have listed the
ebay title for those who wish to look them up.
One point to note is the inconsistent docketing on the first five covers, all of which go to the same address in the same town. Three have a manuscript "Local" and two a manuscript "Foreign" applied by someone unknown. It also shows that docketing for any reason is not 100% reliable.


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Cover 933L


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Cover 933M


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Cover 933N


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Cover 933o


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Cover 933P
These next three have all been forwarded but without the collection of the normally required additional postage for forwarding or return of third class matter. It I believe it was not collected for these three covers due to the belief or actuality that the address change was caused by official orders. When that is the reason then no additional forwarding postage is required.


Canal Zone U10 Uprated Entire with Prexy 118 Printed Matter Rate to CA 932Q 803


Canal Zone U10 Uprated Entire with Prexy 118 Printed Matter Rate Cover 932S 803


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Forwarded Cover 933v


Canal Zone U10 Uprated Entire with Prexy 118 on Third Class Cover 933Q
Lastly here is another one from a different place I picked up. It is unusual as it was first a solo on a PSE, but then it was forwarded within the Canal Zone, transcontinentally. Unlike the three above, the forwarded third class additional postage for forwarding or return was collected. The forwarding postage was shown collected by a 1 cent postage due Canal Zone J25 and without any 1/2 cent dues, a CZ 118 was used. Thus two distinct usages on one cover. Balboa was on the Pacific edge of the CZ and Solo Coco on the Caribbean (Atlantic) edge.

Feel free to add additional examples of the CZ 118 usage as a single as well as single usages of CZ 119, Martha Washington, 1 1/2 cent.