It's a notice CP22A and it says "Changes to your 2017 form 1040A." I spoke to someone at the IRS who told me about the 2 W2s but was unable to offer any other advice.
No, you cannot file a 2017 W-2 with your 2019 tax return. You can only report a the tax data from a 2017 W-2 on a 2017 tax return. You will need to amend the 2017 tax return that was filed to include the W-2's.
See this TurboTax support FAQ for amending a 2017 tax return originally completed and filed using TurboTax - https://ttlc.intuit.com/community/amending/help/how-do-i-amend-a-return-in-turbotax/01/27372
Note - The federal amended tax return, Form 1040X, can only be printed, signed, dated and mailed to the IRS. Any taxes owed have to paid by check or money order and included with the mailed amended tax return.
See this IRS website for a CP22A notice - https://www.irs.gov/individuals/understanding-your-cp22a-notice
If the notice is correct then you do not need to amend the return ... simply agree and pay up. The sooner the better since the penalties and interest continue to accrue.
if the IRS is right and it's not asking for an amended return, you don't need to file.
it would also be impossible to file an amended return without his consent.
the $7,000+ will include late payment penalties and interest which alone can be more than $2,000 of the bill (you should see this on the notice)
you mighty want to consider engaging the services of a pro to see if they can get some of the penalties abated. you might even qualify for equitable relief. since it seems your saying that part of the understatement was due to a W-2 for you not being reported and part due to a W-2 for him not being reported, you won't qualify for innocent spouse relief since some of the balance is due to your income not being reported . there may be other avenues open that a pro can discuss with you,
note that your ex may have gotten the same bill and if part of this tax bill is due to his unreported W-2, why should you pay it all