In this article as far as I understand it, a plugin minor version has to be less than or equal to the Rack minor version. But this article says that you can chose any minor version for your plugin and that it will work with any Rack 1.X version.
I think the first article makes more sense. Otherwise there would be no way for VCV Rack to test if a plugin can be loaded, if it uses new functions and if it is an older VCV Rack version. This would result in runtime error messages difficult to understand for the user, or maybe crashes.
Currently only Forzen Wasteland has a 1.2.x plugin, and looks like there is no plugin > 1.2.x, all other plugins have version <= 1.1.x. So still possible to change the rule, at least with the next VCV Rack 1.3 release.
Of course, this only applies, if @Vortico plans to add public functions in later VCV Rack 1.x versions. If not, then the first article should be corrected to say the same as the second article.