" For property improvements, the available date just doesn't come into play."
But doesn't it, if, "depreciation starts on the date the property is available for rent."
Property improvements, by definition is what must be depreciated, correct? If I can't begin depreciating the building until it's available for rent, then the available date should also affect the new flooring (for example) that was installed between date of purchase and date available. I wouldn't expect to begin depreciating the flooring until the available date.
