Why it’s do rare! From Vox database

This model came out ca. 1967/68 after the Clyde McCoy and before the V846, though there was no actual model name anywhere on the wah some people refer to it as the "Transition" model (from Clyde to V846).
This Transition Vox Wah comes with the clover inductor and tropical fish caps and is the only Vox Wah to use this inductor.
Promotional Record For the Vox Wah-Wah
Some at Thomas Organ, including Del Casher, disagreed with Joe Benaron's decision to limit the promotion of the Wah-Wah to the Vox Ampliphonic line. To that end, Casher collaborated on a promotional recording that demonstrated the capabilities of the Vox Wah for guitar. Dated February 1967, this "punch out" paper record was later distributed to Vox dealers throughout North America to promote sales of the wah pedal. You can hear this recording in the audio player shown at right.

It didn't take long for Thomas Organ to realize that the true sales potential for the Wah-Wah was as a guitar effect. Thomas Organ arranged a press conference in late March 1967 to introduce and promote the Vox wah pedal. This press conference was covered in an article published in the April 8, 1967 issue of Billboard magazine entitled "Big Future Predicted for Vox Invention." Joe Benaron opened the press conference by explaining the Vox Wah Wah pedal could be used "with a guitar or with any amplified instrument or microphone." Benaron also stated that "We are proud to be the company to develop the Wah-Wah, a revolutionary sound."

It is worth noting while Benaron claimed that the Vox wah pedal could be used to "imitate the sound of an on-and-off trumpet," no mention is made of the original namesake of the Vox wah wah, Clyde McCoy, in this press conference.

Now that the Vox wah was being broadly marketed as a guitar effect, the affiliation with an aging big-band leader had become somewhat irrelevant. Most guitarists would have no idea who Clyde McCoy was. Thomas Organ soon dropped the Clyde McCoy name from the pedal, simply renaming it the Vox V846 Wah-Wah in the June 1967 product catalog and price list. As a result, not that many pedals were produced bearing the Clyde McCoy name, making them quite collectible today