The addition "Prov" means "test" - so it is a single piece, not from a series. Other glassworks use the word Unik or Unikat for that.
"Prov" means sample/test, please note that it is not the same as Unik or Unikat.
Please see this thread:
http://www.glassmessages.com/index.php/topic,30355.0.html
