The behind-the-scenes report, published Friday by the Wall Street Journal, sheds new and possibly worrisome light on Tesla’s recent admission that it is dramatically behind schedule on Model 3 production. According to workers interviewed by the Journal, one of the “bottlenecks” Tesla alluded to in that announcement was that body panels were being positioned and welded by hand, rather than by precision robots.

Those robots are in place now, but the workers estimated to the Journal that they might not be fully calibrated for another month.

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It is highly unusual that the Model 3 production line was not fully operational even by early September, more than a month after a Model 3 launch party thrown by the company. Musk did predict at that time that “six months of production hell” lay ahead for the Model 3, but major automakers typically don’t celebrate a new vehicle’s official launch until their production line is fully operational and refined.

In response to an inquiry from the Journal, a Tesla spokeswoman did not rebut the claims, but did question the newspaper’s journalistic integrity.

The Model 3 is a lower-priced bid by Tesla to sell electric cars to the masses, and has been met with massive consumer excitement — the company reported that it had just more than 450,000 preorders for the Model 3 as of this August. Quickly delivering well-built cars to fulfill those orders is an existential challenge for Tesla, as it bids to fulfill its sky-high stock valuation by transforming itself from a niche disruptor into a player big enough to challenge the likes of Toyota or General Motors. Musk has said the company is aiming to build 500,000 cars a year by 2018.

At the current rate of production, it would take nearly 450 years to fulfill existing Model 3 preorders. Both Tesla and Musk have overcome gargantuan challenges in the past, but shifting that horizon — and doing so profitably — might be their biggest yet.