"They switched carriers. Who pays?"

A specific injury

The carrier insuring the employer on the date of injury is liable, and a later change of carrier does not move that. Coverage follows the date, not the calendar.

If two carriers are pointing at each other, that dispute is resolved between them and it does not suspend your benefits. Say so in writing if payments have stopped over it.

A cumulative trauma — this is the different one

Labor Code § 5500.5 limits liability for a cumulative injury or occupational disease to the employers and carriers on the risk during a defined period of injurious exposure preceding the date of injury.

Two practical consequences:

You generally do not have to sue everyone who ever employed you. Liability is confined to a defined window.

And where more than one carrier is liable, § 5500.5(c) lets you proceed against any one of them, leaving them to sort out contribution among themselves afterward. That is deliberate, and it exists so an injured worker is not required to litigate an apportionment fight between insurance companies before receiving anything.

The § 5412 date of injury drives all of it — the date disability and knowledge of industrial causation first coincided, which is often years after the wear began. How cumulative trauma works.

What to do

Write down every employer and every approximate date for the period you did this kind of work. Even approximate is useful.

Keep old pay stubs, W-2s, and union records if you have them. If not, employment history can be reconstructed.

File against the employer you know, and let the carriers be joined. Waiting until you have identified every carrier is how the one-year statute under § 5405 gets missed.

And if any employer in the chain was uninsured, there is a separate route through the Uninsured Employers Benefits Trust Fund — but that Fund is only reachable if the employer is properly joined, and that step gets missed. How UEBTF works.