It was for IBM and Unisys, I imagine.

And then there is the whole DoD security assessment of Multics versus UNIX, where PL/I did play a major role versus C, so the compiler did work correctly enough.

Just this week we're discussing a VC++ miscompilation on Reddit.

IBM are still building and maintaining their PL/I compiler for z/OS, today. Though it is only compliant with specs up to 1979. The '87 ISO is only partially adopted.

I get the distinct feeling it's been a long time since IBM wrote PL/I compilers considering anyone but IBM. So 'correct' here might be 'what IBM needs'. YMMV.