Okay I'm going to do some estimates here based on these numbers:
Assuming 55% of vehicles produced are bound for the US over this entire timeframe, 2017 will end with around 170k US vehicles delivered. With 99k vehicles scheduled to be delivered in the US in 2018, this means car 200k will be delivered in Q2 2018 without any attempts to maximize it. Given that Tesla will be attempting to maximize the credit usage and that I think their Model X numbers are overly ambitious, 200k could be delayed as far as Q4 2018. This means the full credit should end sometime between end of Q3 2018 and Q1 2019.
Model 3 deliveries will be biased towards later in the year in 2018 and I expect nearly all Model 3 deliveries for that year to be to the US, so this equates to about 40k-100k (yes, 100k) deliveries which should be able to take advantage of the full credit! Assuming around 10k pre-registrations (from Space X and Tesla employees + other eligible people) and 10-20k orders from current owners that ordered early enough to be prioritized, there is a high likelihood that everyone who ordered in store on the 31st will get full credit (estimated by me as around 20-30k). In the scenario in which 100k full-credit deliveries are made, nearly everyone who ordered before the event could get full credit.
I think these numbers are still a little conservative now that Tesla has said they are ramping up production. If they spin up the lines faster, there could be as much as a 50-70% increase in Model 3 deliveries in 2018, which could result in another 10-40k eligible deliveries.
All this being said, I think it's fair to be optimistic for the people who ordered as fast as possible.