An interesting couple of anecdotes on who knew what, and when - here's an excerpt from Wikepedia's article on the Intel Management Engine:
SA-00086
Some months after the previous bugs, and subsequent warnings from the EFF,
[4] security firm Positive Technologies claimed to have developed a working
exploit.
[83] On 20 November, 2017 Intel confirmed that a number of serious flaws had been found in the Management Engine (mainstream), Trusted Execution Engine (tablet/mobile), and Server Platform Services (high end server) firmwares, and released a "critical firmware update".
[84][85] Essentially every Intel-based computer since
Skylake (which was launched in August 2015), including most desktops and servers, were found to be vulnerable to having their security compromised, although all the potential routes of exploitation were not entirely known.
[85] It is not possible to patch the problems from the operating system, and a firmware (UEFI, BIOS) update to the motherboard is required, which was anticipated to take quite some time for the many individual manufacturers to accomplish, if it ever would be for many systems.
[17]
And here's another on Intel's CEO Krzanich stock sale (note the dates as compared to Intel's public confirmation of ME problems on 20-Nov):
http://fortune.com/2018/01/05/intel-ceo-stock-security-flaws/
If Apple exec's start dumping Apple stock shares, watch out. Now that the bird's out of the hat, so to speak, all of these chip and computer hardware vendors need to be as honest and forthcoming as possible about when these flaws were known, and what the ramifications may be for the computer industry. The need for secrecy for the sake of security is no longer an issue with SA-00086.