More confusingly, at my first (tech industry) jobs the progression was Jr -> no modifier -> Staff -> Senior -> Principal, "Staff" being the first level you could start coasting at, "Senior" being the end for most people who kept developing their skills, and "Principal" for extremely autonomous / R&D roles / "Leads" with no actual teams. In this case, "layoff protection" was exactly what the staff level was for; you were also expected to hit it in 3-5 years.

Now it seems to be Jr / n/a / Senior / sort of equal footing for Staff/Principal depending on whether you're a generalist or specialist? And Staff might also be Lead but also not? I've read Larson's stuff and I'm still not sure the moniker is useful in a way "Senior" wasn't, except to the degree other titles have inflated. (I've seen three resumes in the past week for "senior" applicants with 2y experience or less restricted to a single stack.)