small tax cards that arrived in my mail to determine my basis. To make things simple they said the land was worth 100,000 and the building was worth 70,000. So I’ve been depreciating 70,000 as the basis for a few years now.

I just found out I could’ve used the original purchase price of the unit? let’s say that was $200,000. 

So I’m confused.. what’s my depreciation basis? 

Is it 200,000 aka my original purchase price?

or is it 200,000 minus the land 100,000 = 100,000?

Or what the tax card said = 70,000?