Samsung SDI is separate enough from the smartphone makers that I'd guess it just wasn't prioritized as much as it should have been. 2.5 million phones were sold

Samsung SDI is separate enough from the smartphone makers that I'd guess it just wasn't prioritized as much as it should have been. 2.5 million phones were sold, at 14 watt hours per battery that means that the Note 7 batteries would only be a few percent of their total production (35 MWh of Note 7 batteries produced.) Catching problems like this can be pretty tricky and at the end of the day it's also possible that a few people getting lazy and programming the machines wrong led to this.