The same keyword can be part of multiple keyword declaration overrides. This is because keywords are atm not restricted into a single specific keyword set. I.e. one shader could declare #pragma multi_compile FOO BAR whereas another could do #pragma multi_compile FOO BAR BAZ. To override both of these we'd need two different keyword declaration overrides to target the exact set of keywords given in each pragma. To be able to do this, the system needs to allow using the same keyword on multiple overrides.