So then the next decision point will be what version is available to deliver by 3/31/19. .
No, 3/31/19 is not an important date at all. Tax credit remains at $7500 through 12/31/18, then is $3750 from 1/1/19 - 6/30/19, and then is $1875 from 7/1/19 - 12/31/19, after that it's all the way phased out.