Bands are usually per level - if someone is sufficiently good you bring them in as a Principal/Staff/Magic Unicorn/whatever.
This leads to the same phenomenon where you need to work for 2 years to get promoted but if you jump ship your new manager will set your level in line with your salary expectations. And of course the levels are largely meaningless outside of compensation and office politics.
At my original company I was performing Senior-level work (like, literally according to the staff level formalism from HR). But I was told by my manager that to be classified as a Senior-level staff, you have to have been performing Senior-staff level work for at least a year. Therefore being promoted within the organization is a long process. Moreover, with the usual 1-3% raise, you're still in the (low-end) of the pay band for Senior staff, so from management's point of view there's no real problem.
.. and then of course, if you're hired in, you just have a few phone calls, couple of interviews, discussion with the hiring manager and you're at a pay-level and job-level far ahead of existing employees even with identical experience.
This exact scenario happened to me - I was a "senior manager" by HR title but I was actually just promoted to team lead in practice. I meant to illustrate the setting of compensation happened almost entirely without engineering input at a company level (in my experience, where I worked, etc.).
This leads to the same phenomenon where you need to work for 2 years to get promoted but if you jump ship your new manager will set your level in line with your salary expectations. And of course the levels are largely meaningless outside of compensation and office politics.