If you are filing paper forms, send it with your tax return. They get just the quarter that says Federal copy B. If the IRS doesn't like it, they will either contact you or your employer to get a replacement. If they contact you, tell them that that is what your employer sent.
The IRS might make you resend a form if they don't like it. So long as you pay the taxes correctly though, you won't owe additional money. They'll just ask for the right form. In this case, it is your employer's responsibility to send you the correct form. So at worst this would require writing a letter explaining that this was the form that your employer sent you.
I wouldn't bother sending the letter now. Let them tell you if they think the form is wrong. Then send the letter in explanation if they do. They should get the right form from the employer. Or they should make the employer send the right form to you, which you could send to them.
Here's what I think will happen. Someone at the IRS will look at your form, check your math, and check that the data matches their other source (your employer). Assuming that the employer sent a valid copy to the IRS, everything will match. That person might notice the preview and think it is goofy. I very much doubt that it would cause a problem at that point. The primary purpose of sending those forms is to show your basis for your income and tax claims on the return. If everything matches, a minor misprint on the form is not going to be an issue.
And as someone already said, if you are e-filing, you don't send your paper copies. You just type in the information when asked. So all this could be moot.