Normally, when you stop using a vehicle for business, you must recapture depreciation expense taken in past years, as taxable income.
Alternatively, when you trade in a vehicle, instead of recognizing a gain or loss on the sale (related to business use portion) and recapture of depreciation, there is a special calculation for the basis in your new vehicle to defer the gain or loss. This treatment is for like-kind exchanges reported on form 8824.
In regards to your first question, yes the software will account for the use of the vehicle from 2014 - 2016 to calculate what depreciation recapture would have been at 100% depreciation for excess depreciation and the carryover amounts for the basis in the new vehicle.
See this info at the IRS Pub 463 for vehicle dispositions, here: https://www.irs.gov/pub/irs-pdf/p463.pdf
