A lonely Thonet chair.  

I picked up this Thonet stacking chair in Rochester, NY in 2000. I've never seen one like it before or since. Intermittent internet searches throughout the years have been fruitless. I've often wondered if this is because the chair is rare, or if it so pedestrian so as to deserve no attention. I've also wondered about the number 218 stamped on the underside - I think it's an institutional owner's mark for inventory. I guess my queries are: has anyone seen one of these guys before (if so, I'd be curious to know where), and does anyone know anything at all about about this design?
<img class="wpforo-default-image-attachment wpforoimg" src=" http://old.designaddict.com/sites/default/files/forum/IMG_4255.