D7150 added this text ("a revision's reviewers can always...") and I said it "wasn't true but would be soon", but never made it true.

The easiest fix here is probably to delete this line of text, since no one appears to have relied on the behavior for almost four years and implementing the behavioral change runs into complicated questions in T4411. It might still be appropriate eventually, but probably best if tackled adjacently to that stuff.

We require the "a revision's reviewers can always..." behavior. Please implement it instead of changing the text.

In our workflow we make reviews private to group projects (they represent departments), via herald. Occasionally we have cross-department reviews in which case the reviewers need access even if they are in another department.

The plan forward here is to correct the text. I will follow up with you on Discourse.

See T13602 for eventual followup.