What causes a property assessed value to drop 15k?

[Steven J.]

i'm doing some research on a property in a smaller rural town. In the past, under ownership of a long time owner followed by Wells Fargo the property assessed for 34,100 in 2011. After it changed hands to a CPI Housing Fund based out of California the value dropped to $19,000.

What sort of thing caused this? The seller is hoping to get 40k, which I can't meet him at. Would any one recommend I bring up this bit of knowledge I found or not?

Thanks,