I only wrote the following in response to Mike Kone:
Mebbe so, but what about those open C dropouts. Wouldn't these pre date the dropouts with the spring holes?
Jay Sexton Sebastopol, CA
To my eyes, the frame looks nearly identical to the one I had on ebay last week that didn't hit $700 (sold later off ebay for a good bit more, all very surprising). The dropouts on Dale's bike do look like later ones (the clue to the one I was selling as likely having had a dropout replacement I think). The one I sold was certainly built around 1959 to 1961. I'd peg the date of the bike in question as being from 1958 to even as late as 1967 - with the dropouts pushing the build date to the later period as wise Harvey Sachs points out.
Cinelli Serial numbers from what I can tell are generally meaningless - a "stroll" through the Cupertino log book years ago showed very weak correlation between year and serial number, although bikes sold in very close time to one another often had close numbers. But those batches of similar numbers were not sequential. Quite maddening!
Another clue would be if the bike in question accomodated the reproduction headbadge without difficulty - if so it is a late 50's bike or later. The really hard-to-find earlier bikes used a larger size headbadge with screws for fastening farther apart.
Mike Kone in Boulder CO