Does the a W-2 form for an employee pull in all payroll for an EIN even if I didn't own the business for the whole year

Thanks for asking us here in the Community, @miller3525. 

Yes, the W-2 form for an employee will pull in all payroll since you bought the business entity in the same year. See article: Changing your business entity.

To separate the new EIN from the old one, you'll need to set up a new payroll account. You can check out this article for more insights: Get started with Payroll.

Let me know if you have additional concerns, @miller3525. I'll be here to help you more.