Apparently Sauer made a few early models without a top extension lock-up. Note the "Eagle" on the under side of the left tube as well as the initials near the flat & lower rib juncture:

http://www.auctionarms.com/search/displayitem.cfm?itemnum=9516324

I've probably stated it once too often already, but the craftsmen in the Suhl/Zella Saint Blasii area were on par with any in the world.

Kind Regards,

Raimey
rse