An easy way Bloomberg could support their story: allow one or more of their "senior insider" sources at Apple/Amazon to speak with another outlet (AP, NYT, whoever) who agrees to maintain their anonymity.
> Joe FitzPatrick was not one of these 17 individual primary sources that included company insiders and government officials,
What you're suggesting involves both violating the trust of the source and creating the impression the news organization needs its competitors to establish its credibility. I can't imagine this is anything short of a complete non-starter for Bloomberg, an actual serious news organization.
I agree that it seems tricky for them to go to their sources and ask them to talk to some other news org however.