w/o a botanical latin name.. its hard to look it up for you ...

perhaps your blue version is sterile ....

as the breeders move from the plain old color [red???] .. to the more exotic.. it is very common for the end effect to be that the plant is sterile ....

that is presuming that your z9 trumpet vine.. is the same plant i know as trumpet vine.. here in z5 MI ... common names can be very problematic ...

if you dont have the name.. a pic might get you an ID ...

ken

Here is a link that might be useful: how to post pix

Why not take cuttings? Most vines root easily and it would be much quicker than growing from seed. (Is it Distictis 'Rivers'?)

Is this your vine!
Distictis rivers * Royal Trumpet Vine

It is Distictis Rivers...I hadn't thought of cuttings because of the size of the plant, but it's probably time to try that. However, I just want to know what it takes to get this trumpet vine to produce seeds. It's become a challenge to figure this out.

The only thing that I can come up with is that it needs the right pollinators before they will make seeds pods. Seems that the Humming Bird is the #1 pollinator for this plant.
Hope this helps