How do you resolve box b on a w2 if it was returned because the company's EIN was issued after the tax year?

Box b on the 2018 Form W-2 is the field for the Employer Identification Number (EIN). The inclusion of the EIN is a mandatory element on every Form W-2. The IRS cannot process a W-2 without it. If it truly is missing from a form you have received, I suggest that you contact payroll or accounts payable office and request a replacement Form W-2 containing all required information.