1915 Expo Postcard From Bureau Of Engraving & Printing

In recent months, I've been hard at work putting together a huge number of scans for the online image catalog of the new Souvenir Card Collectors Society website (http://www.souvenircards.org/gallery/gallery.html). In the process I've made a lot of interesting discoveries.

Souvenir cards are distinguished from other material by what they are not, and one of those "nots" includes things intended for postal use, such as postcards. However, I discovered some rule-breakers in the "Forerunner" category. In 1915, the Bureau of Engraving & Printing brought their exhibit and demonstration press to the Panama-Pacific International Exposition in San Francisco. The BEP attended a number of these expos during the early 1900s and typically distributed or sold souvenir cards and engraved silk handkerchiefs at them. But for the PPIE, in addition, they printed engraved, postcard-sized cards showing a number of Washington, DC, buildings. From the inscription on the back, these do appear to be formatted for mailing, if desired.

I personally own one of these cards and have scans of a few others. I've never seen any of these cancelled. They are genuinely rare, by postcard standards. Has anyone come across others like this?

Here are three others in the set, all with the same text on the back.