I'll bring this to his attention, thank you. 

"What do the prior years' tax forms show for how this got handled? Were the prior W2s also like this?"

Because he gave me the payroll transaction history for 2018-2019 in one file, I didn't tie it back dollar-for-dollar to his 2019 w2; but, the accountant from the company said that the accounting firm they use to prepare the returns and payroll has been doing it this way for years. 

I think my best course of action is to bring this error to his attention, report the wages as indicated on his w2 and not deduct the health insurance premiums. It seems by doing this I have done as much I can and the rest should fall on the employer to investigate. Fair?