My apologies but I realized while I was in bed this morning that I remembered the rules incorrectly. For the state tax credit, you should still be able to file for it next year even if you don't register it until early 2019. I remembered that with my first Teslat that I bought in December 2016, I didn't register it until February 2017 but was able to file for both the federal and state taxes credits when doing my 2016 taxes. The state tax credit
does need proof that you registered the car in Colorado but it doesn't need to be registered in the same year as purchase. Again, my apologies for any confusion I may have caused!
Since I just got another 60 day tag, I may wait until January before registering the 3 but will stop claim the 2018 tax credit.