It seems like this should be obvious, but based upon all the questioning of Tesla missing a production target of 1500 units at the beginning of an S-curve type ramp up makes me realize it isn't.
Some problems and delays are impossible to predict, but completely normal and expected in any new process. So, Elon used a well tested method, the S-curve, to predict production ramp up. Even if you can't predict specifically what will cause delays, you can anticipate their impacts on number of units produced to some extent. The amount of optimism/pessimism the estimator uses to draw the S-curve will be a guess at best. However, the bottom line is that a small number get produced at the beginning and momentum builds over time. (Again, I feel like I am stating the obvious, but the evidence says I'm not.)
So, if Tesla misses forecasts by 1200 units (yes I know this is 80% percent of the forecast and 400% of the units produced), it won't matter when they are at full production. When they are producing 20,000 units a month is it inconceivable that they might produce 22,000 in a month and wipe out any backlog from missing in September. The point is, the small numbers anticipated at the beginning make it easy for skeptics to claim the sky is falling when they are missed by a little bit.
Now, if delays continue and are drawn out for several months, there is a problem. But, you can't predict success or failure at this point based upon these tiny numbers. (See Chaos Theory in Wikipedia.)