Went to the IRS site to review the tax credit forms IRC 30D New Qualified Plug-In Electric Drive Motor Vehicle Credit | Internal Revenue Service and see where it is only showing models up to 2019 as qualifying:
I would imagine that they just haven't updated their website. Government is slow on these kind of things. As long as you took delivery in 2019 you’re good.
The model year is irrelevant. The date “placed in service” is what’s important, and as long as it was in 2019, a model “year” 2020 Tesla qualifies for a potential tax credit.