Depreciation: not going to happen on Star Wars sets that are not longer in production.
Water damage: Lego is water proof.
Breakage: being easy to take apart and put back together is Lego’s core principle.
Edit: wait, the whole collection was sealed and new in box. Yea, just water damage to those boxes would cut the value by at least 10%. Collectors are picky as shit.
I didn't realize people bought Lego to leave in the box. But I guess I shouldn't be surprised because it's a common thing for collectors to do in other hobbies.
Given this was a set of full star wars legos with decades of age a lot of those bricks are already going to have degraded somewhat and technix style components are likely to be significantly damaged from internal sediment accumulation. If you drop your water proofed water in a stagnant pond for three weeks it's likely that the internal seal will hold up and protect the delicate components but you'll probably need someone to pull the glue or other sealant out and replace it as well as going over the exterior surface with cleaning solutions to get it back to the quality it was in before being submerged - and flooding is rarely an instantaneous affair.
I wouldn't underestimate just how damaging to goods storage can be - and if you're doing it at scale you're going to be paying that cost constantly just as a percentage of value stored.
So I don't think I'm underestimating the resilience of Lego bricks to flooding.
There was an article a on HN a while back about the plastics chosen by Lego. They put an exceptional amount of time and effort into choosing durable materials for their bricks.
That said, I'm surprised Lego survive outdoors. My understanding is that ABS is not UV-resistant.