Too strange. Live and learn. I'll stick with a commonality that is supported on all the saxes I play. Voice and intonation across all the saxes I play are enough of a challenge without added custom keyworks.
The curved soprano I had was an Evette-Schaeffer System horn: it had interesting alternate C#/B/Bb keys "above" the low E & D keys and has similarities to the Apogee System.
I think I wasn't clear enough in my original post.
I wouldn't call that a low Eb trill, at least in the sense of the dedicated G# trill.
When you depress 123 | 1 and then the "pearl" that's attached to the D key, that should sound an Eb. It's not the traditional forked fingering of 123 | 13, but it's close and can be fingered as such (if you see the ad on the E&S System page, it describes it in better detail: Buffet wants you to finger the "forked" Eb 123 | 12, with your middle finger on the little "pearl" I mentioned).
And it's still an Eb vent in an odd location, not like on most horns, which would have been on/near the bow on the left side (as you're playing).
According to the Apogee ad, the RH little finger plays B with the extra key!