When KB4019926 was released I was able to install it in my QC environment which is set to fast ring. My production environment is set to slow ring, and therefore will not install this KB. When is the rollup scheduled to be released for slow ring?
I don't completely understand the issue. Configuration Manager doesn't have the concept of a being in a permanent fast or slow ring. You opt-in to see a particular major release earlier or wait. This has to be repeated for every release.
This update rollup (KB4019926) was not targeted to specific builds of 1702. Everyone who has 1702 should get it. Unlike KB4018732 which was specifically for those who had opted-in to the first wave of 1702.
Perhaps I'm missing some information about your environment.