Hi - I think you may have looked at the wrong caption in Miller's - and your comments regarding the Rembrandt Guild refer to another, albeit similar funnel shaped vase/bowl, at the top of the page.
Whilst Pitchford did apparently design both pieces, your design is the late 1940's item, which as far as I'm aware, and going on the information in Benson & Hayhurst, and Charles Hajdamach, does not appear to be associated with the Rembrandt Guild.
Pieces which have that association have the appropriate back stamp indicating that connection.
If it's any consolation, Miller's give a higher value to your later design than the earlier Rembrandt piece.