How would I determine the market value or blue book value of my vehicle during a previous year (when I started using it for business)?

[KatDesign]

The answer to this question that has been posted simply says to reference FMV information published for that year, but where can that be found?

Another answer said to look at the value for 2 years newer, which does not make sense to me.

[LindaB1993]

According to current depreciation rates, the value of a new vehicle can drop by more than 20 percent after the first 12 months of ownership. Then, for the next four years, you can expect your car to lose roughly 10 percent of its value annually.  

I recommend researching the current book value and adding 10% per year for the previous years based on the above industry standard.