Pepper finally boasts - but when?

The word "Sousaphone" shows up in a big way in this advertisement that I'm told was inserted as a loose page in an issue of Pepper's Musical Times and Band Journal - perhaps the one noted in the post below (early 1896), but it could have been a bit earlier, or a bit later (the folks at Pepper today thought it was 1893; my guess is that it was either in 1896 or a bit later, given that Herman Conrad's endorsement in the 1896 Journal doesn't yet specifically speak of the Sousaphone, like it does in the advertisement below):

(Image courtesy of the Museum of Making Music and the J. W. Pepper Co.)

Since it's very hard to read what it says at the bottom of this document, I'll provide it here:

THE SOUSAPHONE. MADE BY J. W. PEPPER.

This instrument was made from the plans and under the direction of the famous bandmaster, John Philip Sousa. It is an original idea of his, and he considers it the best method and only correct way of obtaining the full tonal quality of the Helicon BBb Bass in band. We feel proud of the honor that Mr. Sousa has conferred in selecting us, from among the large American band instrument manufacturers, to receive the order for making this special instrument: thus showing his confidence in our ability to successfully make a perfect Sousaphone. The instrument is played by Mr. Herman Conrad, the first BBb Bass of Mr. Sousa's band. The other larger instruments used in this band were also made by Mr. Pepper. The Sousaphone is a Helicon BBb Bass of the largest size made.

And at the very bottom of the page is the following:

MR. HERMAN CONRAD'S TESTIMONIAL.

Mr. J. W. Pepper:
Dear Sir - the Sousaphone is admired everywhere and gains in reputation daily. It is in splendid tune and tone and has a wonderful carrying power. It proves an irresistible attraction.

Yours very truly, Herman Conrad

The insert does say, in the upper right corner, that this Sousaphone was  "used daily in Sousa's peerless concert band." And Conrad, in his testimonial at the bottom, adds that it was "admired everywhere and gains in reputation daily." It sure sounds like the horn was active in Sousa's Band, perhaps for some time. So why don't we hear about it anywhere else during this time period? I have not yet been able to locate any other reference to this  "irresistible attraction." Strange.

Further, I have not been able to locate any photos of Sousa's Band from 1894 through 1897 to confirm that this horn was played in it for all or part of that time. The earliest photo that I have found that shows a Sousaphone in use is from 1898, and it reveals an entirely different Sousaphone - one presumably made by Conn. And the buzz around that horn makes it seem as if it was the first to appear (more on that shortly). Again, strange. Why did Pepper's Sousaphone essentially dissappear?

[UPDATE on this important page from 2015]