I think part of the confusion (at least for me) is that there are two independent version numbering systems: one in /etc/os-release, and another in RPM macros.
The RPM macros have increased without a big gap, and will not go backwards. OBS and the package building is probably happy. Nothing unusual is happening there. Probably the same with zypper, as it uses the information in the RPMS. Of course, any RPM install-time scripts that might get run could potentially be confused if they rely on the OS version to get something correct.
/etc/-os-release has increased with a big gap (13.3 -> 42.1) and will perhaps now go backwards (42.2 -> 15.1). Everything outside of RPM/zypper is potentially messed up. This includes Makefiles, shell scripts, and probably most things outside RPM/zypper. It is this type of stuff that I am most concerned about.
OOC, is there any reliable way outside RPM to get access to the version that RPM would use? Something other than /etc/os-release?