The filing states that zero Model 3 beta prototypes were built prior to December 31, 2016. The filing further adds that production of said prototypes is among the goal of Q1 2017 (ending March 31, 2017).
Additionally, this statement from the filing confirms that production Model 3 beta prototypes is "currently" underway:
"We expect that the next performance milestone to be achieved will be the successful completion of the Model 3 Beta Prototype, which would be achieved upon the determination by our Board of Directors that an eligible prototype has been completed. Candidates for such prototype are among the vehicles that we are currently building as part of our ongoing testing of our Model 3 vehicle design and manufacturing processes.“
Just how long it will take Tesla to move from beta prototype to production of consumer Model 3s is anyone's guess at this point. However, Tesla's timeline calls for production of the first real Model 3s to begin in July.