Eureka!! I finally found a way to update from build 16199. It has taken over a month. I tried everything under the sun that is recommended everywhere, to no avail. Finally, I found a site that suggested an in-place upgrade. I downloaded the ISO from Microsoft for build 16232 from
https://www.microsoft.com/en-us/software-download/windowsinsiderpreviewadvanced?wa=wsignin1.0

