But how would that be different for an owner who performs all the preventive mx he can legally sign off then sells the aircraft? He would follow the same Part 43 guidance you do under your A&P where he could legally refurbish the entire aircraft inside and out under his PPC and would be liable for it until it was refurbished again. Your A&P simply allows for a larger range of task to perform. And just for context, I'm still technically liable for all my past mx and I seriously doubt my previous policy providers would be liable since I'm not a current policy holder. Regardless, just trying to see what you see especially from an owner standpoint with preventive mx.
I think it's the same, and to your note, you're restrained by your certificates to meet their definition of "legal maintenance" -- but the owner policy will allegedly cover you as long as you act within those limits -- so preventative mx for an owner, full scope for me as an IA, but I would think zero coverage for an owner who did A&P things without those certs.

That owner would of course need to log their illegal deeds to be discovered, to be sued. Invoking the "Squawk Fairy" and not being discovered is probably stronger coverage than whatever my owner policy provides ($1mm).
Owner policies do have a duty to defend for acts committed during the policy coverage period, so I think that's a LOT stickier for mx work than pilot misdeeds -- I don't think they've considered the position very well by including it in the liability coverage, honestly. Still, as long as they're mortally afraid of being found acting in bad faith, I expect they'd brass up if I got sued for the motor I hung 3 years ago

Then they'd add new language excluding maintenance actions after they paid out a million.
What I think happened in my case is my broker asked a clarifying question of my underwriters (STARR) which created sort of an override/exemption and paper trail of their acceptance/acquiescence. The policy language itself is somewhat fuzzy. These are the important parts:
IANAL but it appears to me that liability (for the insured) is covered for anything caused by the maintenance on the airplane, irrespective of who turned the wrench.
There is an even murkier situation where they will cover liability up to 1 year after the sale of the plane -- so not as infinite as I had remembered --
Two important notes on the above -- D2 is a bit nasty as they're calling out that they will not cover situations where the maintenance was found inadequate. (and I'd argue that's the hottest seat for one doing their own maintenance -- an onward claim that it was deficient)
A2 means no intent for profit -- so this gets a little hinky with an LLC owned aircraft like mine -- I can't charge my LLC for my A&P time as it would imply a profit motive and negate whatever coverage is here.
It is D2 above that itches my brain, though, and why I asked my broker to clarify. Her email (right or wrong) interpreted the policy to mean they would defend me against such an allegation, but not in the case of gross negligence like a pencil whip/fraudulent mx. If she got it wrong, her own broker Errors & Omissions policy will be summoned to cover her misinterpretation and pay my legal bills
Woof though. It's not a straightforward situation and needs some mental gymnastics. Best to ask the broker to lay out the cases where it does and does not work and rely on their interpretation/carrier answers (and ultimately E&O -- don't let them hand-wave away answers, pin them down in writing/email). Not all carriers have the language above.
$0.02
