AFAIK: The first three numbers are YYQ, where YY=Year as 20*21*, and S are "Quarter" (it may vary between 3 or 4), the next is the actual kotlin release number 1.5.0 (or any 1.5.x), the next is an indicator that the plugin is released (or not (experminental, debug, or [blank](!)) - XXX- is a kind of running number for the plugin, IJ (IntelliJ) or AS (Android Studio) refers to the build# signature in the About box of your IJ or AS version (mine AS reads now: Build #AI-203.7717.56.2111.7361063), the second number "7717".
NOTE:!! DO NEVER TRY TO INSTALL AN IJ MARKED VERSION ON AS, this will render the common plugin file area in AS useless. The only remedy is to install a PRIOR version (with another "second" version#), and go for the bundled plugin AS, and update from there on...
Stay put with IJ's on IntelliJ and AS on AndroidStudio.