FWIW I was L5 manager (on the SWE ladder) in two PAs. The L6 requirement did exist but in my experience was quite soft. All that my management had to do was justify to the VP that I was capable of doing the job and would soon be ready for promo to L6 (though the first org got nuked and the promo took a long time).

Interesting. Where I was I never saw an exception to the L6 rule.