Same would apply if he'd kept a TV or fridge or car in its crate that long...
Rgds
Damon
Depends on if it's a 1989 Ferrari, or a 1989 Toyota Tercel...
As long as they're intact and test OK, I'd rather see those panels go up and be used - if only so that the sunk cost of purchasing them isn't wasted, but also I don't like seeing things go to waste.
Some identification may be found on the panels themselves (sticker, data plate), despite losing the labels on the crates.
From that you could judge the amount of degradation, if significant.
This neighbour of yours, who seems willing to spend thousands of dollars on stuff he doesn't use... sounds like someone who needs to be convinced to get an outdoor pool... maybe a sauna...
Good luck!