Sounds like someone wanted a shinny new toy for Christmas and couldn't wait a couple days more.  For the lack of patience, the old rule on phaseout will apply, I'm afraid - unless it was delivered in 2023.

It's not the model year that matters.  References made in §30D and the IRS guidance are to purchase date, delivery date, and placed in service date rather than model year.

There are some different provisions by year, and for the signed sale contract.

Are you using the IRS resources available on the web?

2023: https://www.irs.gov/credits-deductions/manufacturers-and-models-for-new-qualified-clean-vehicles-pur...

2022: https://www.irs.gov/credits-deductions/manufacturers-and-models-for-new-qualified-clean-vehicles-pur...

You need to evaluate if each purchase qualifies and what it qualifies for and which tax year applies.

And the salesperson told them they could get the credit.

"And the salesperson told them they could get the credit."

In both tax years!