Received some particularly useful information via email.

TOST replaces the stock valve on the tubes they use in their wheel
assemblies. There is no indication of the change on the tube; however,
the valve is marked. When ordering, it is important to note the valve
imprint (as opposed to the stamp on the tube itself). I should note
that the original tube (the one I replaced) developed a leak along the
seam of the vulcanized, non-standard valve. I plan to inspect these
tubes carefully in future before putting a new one into service.

For my Ventus 2bx, the valve is marked as follows:

Alligator
TR88eq
Made in Germany

This is the short valve stem with a 90-degree bend. The double bend
long stem valve from the Nimbus 3 tube also works, though clearance
with the gear strut is marginal.

Many thanks to PSU, who kept me in the contest at Uvalde by lending me
his spare.

Thanks all for your help.