The Geneva tenor trombone:
https://www.geneva-brass.eu/en/instrume ... mbone.html
looks an awful lot like the Cerveny VFC-SL6677HR
http://www.vfcerveny.cz/en/piston-valve ... fc-sl6677h
Cerveny's website only lists four-valve basses. Amati (Cerveny's parent company) lists a couple basses on their site, but nothing like the Geneva The Geneva bass shares the curved handbrace with the Geneva tenor (which may have been inspired by the similar brace used by Kuhnl & Hoyer), but it also has the Rath-style clamp on the tenon joint.
Could be a prototype or a development horn. Maybe not a knock-off of any particular model, but more along the lines of "borrowing" bits from several other manufacturer's existing designs? Hardly anyone starts with a clean sheet of paper (though those that do sometimes achieve great things).