I thought I saw the topic discussed in AMT magazine (for A&Ps), but I never looked into it. I haven't exercised my license for a while.
I did remember it because, it is one of my pre-conditions for working under my license in GA. At large airlines they work mostly under a carriers certificate which is why they sign for their work with an employee number instead of their license number.
They are still responsible in a punative sense, but the airline has the deep pocket.
A few of the guys at the Commeriative Air Force hangar next to the FBO were recruiting help and I asked them if they had any coverage for their free work on the old warbirds. They haddn't looked into it.
They were just buttoning up the Sea Fury they keep there. A couple days ago, I was out pre-flighting when the local F4U Corsair did a flyby and landed too. I love watching those old muscle machines. Great to have folks in the neighborhood with real money.