Can I add another W2 after I’ve filed?

You will likely need to amend your return.  The IRS will also get a copy of your W-2. If it is not reported they will likely invite you to explain why.

However, slow down. You obviously filed early without all of your documents (FIs have until 1/31/19 to put that information in the mail to you.)  The amended return form 1040-X will not be available until mid-late February.  And, you CANNOT e-file an amended return, you must PRINT and MAIL it --it usually takes the IRS 2-4 months to process an amended return.

Finally, you need to WAIT until you find out if your return has been REJECTED or ACCEPTED.

If it has been rejected then you can simply make the corrections required to fix the rejection AND at the same time add the information from the W-2, and re-submit your CORRECTED e-filed return.

If it has been accepted you will have to prepare, print, and mail an amended return ---BUT WAIT until you receive your refund before filing the amended return .

When mailing a printed return it is always a good idea to go to the Post Office and mail it 'Certified' with 'Return Receipt'.  That way you will have proof that they received it and when it was received.