Sorry, I assumed ANCS was included in v1.5.1, but I realize now that it's a new sample being introduced in v1.6.0.
RC stands for "Release Candidate" and is a common term used to describe the final stages of a SW release cycle. Here is an excerpt from a Wikipedia article explaining the term (https://en.wikipedia.org/wiki/Software_release_life_cycle):
"Release candidate
A release candidate (RC), also known as "going silver", is a beta version with potential to be a stable product, which is ready to release unless significant bugs emerge. In this stage of product stabilization, all product features have been designed, coded and tested through one or more beta cycles with no known showstopper-class bugs. A release is called code complete when the development team agrees that no entirely new source code will be added to this release. There could still be source code changes to fix defects, changes to documentation and data files, and peripheral code for test cases or utilities. Beta testers, if privately selected, will often be credited for using the release candidate as though it were a finished product. Beta testing is conducted in a client's or customer's location and to test the software from a user's perspective.
Stable release
Also called production release, the stable release is the last release candidate (RC) which has passed all verifications / tests. The remaining bugs are considered as acceptable. This release goes to production. Some domains (for example, Linux distributions), have two types of stable releases: normal, or stable releases and long-term support (LTS) releases which are maintained for a longer period of time."
