Yes, this is public information... Go to https://3rdpartysource.microsoft.com/ then filter using Sphere 19.07 to access the source files for the latest OS 19.07 version
I'd recommend posting that kind of question to the Microsoft MSDN Azure Sphere support forum (Avnet provide the hardware platforms (Starter Kit and Guardian), Azure Sphere certified modules and MT3620 chip-level devices, the OS is from Microsoft...) https://social.msdn.microsoft.com/Forums/en-US/home?forum=azuresphere
And I was hoping for more!
