I'm wondering if he can get away with just correcting the basis on the 2015 return, since we're only talking the previous 3-4 years that are wrong. What that would do is significantly reduce (or even eliminate) the 2015 depreciation taken, because of what would be excess prior depreciation.
I know I did this on one of my rental properties, but I corrected my basis in the 2nd year (2nd full year) so it didn't reduce the 2nd year deprecation by that much, and didn't really "stick out" as far as I could tell.
