how do you prove the timing? that it happened at the time of construction and not after?

You get one of the people who did the installation to admit to it. I'm sure you could find someone who has a conscience or doesn't think they are personally at fault who would be willing to own up to it.

Construction crews in Arizona? They aren’t going to own up to anything because a majority of those workers are in the country illegally. You aren’t going to find them going to depositions or signing affidavits any time soon. That isn’t mutually exclusive with “having a conscience” of course, but that does mean that you aren’t going to have much luck finding anyone who actually worked on that crew and if you did, they aren’t going to talk.

I can only speak for UK contractors/companies, but most of these guys will immediately close ranks on you if you try and pull this. The guys at the lower end of the chain won't want to say anything because it could affect their ability to get work at a later date. A lot of them are on temporary contracts, and these companies talk to each other. If they start making noise about these sorts of mistakes, they could well wind up on a blacklist.

With the chaining of subcontractors, I doubt you'd even find the company that did the work, let alone an employee.

Expert testimony.