Search and ads, at least, had the L6 requirement for manager going back as long as I’m aware. I was under the impression that the requirement was relaxed at some point in some of the less revenue critical orgs, but that the L6 restriction actually goes back a long way.

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).