The Vade Mecum doesn't have anything special to say about the 16.5cm length, except to list it among the other focal lengths used in f/4.5 for the various Bergheils. I think Compur shutters were used on the Bergheils, so it could be original if it's a prewar Compur (the one on eBay certainly isn't!). Maybe it was sold as an auxiliary lens for the Bergheil, one of whose virtues was interchangeable lenses.

In any case, if it's from that series as the Vade Mecum indicates, it should be "one of the good ones" for sure. The 13.5 on my Bergheil is scary-sharp. I have no clue what the market will bear for the lenses in isolation, but if it is in fact in Bergheil bayonet, I'm going to have to see what you decide to ask for it and how my tax refund looks!

-NT