You are always responsible for your own correct tax. The accurate calculation guarantee may or may not cover penalties and interest in this situation, but frankly, every taxpayer has the responsibility to double-check their return before they file it. If you made $60,000 and your income was showing as only $40,000 (for example) you should have asked questions before filing. And some employers don't even put their W-2s on Turbotax at all, lots of people have to manually type in their information. We don't even know if this is Turbotax's fault, maybe the employer only put one W-2 on the server. It's also irregular that they would issue 2 W-2s for a change in status (like part time to full time?). (It's a bit more common that if you change business units and they use different payroll processors, you might get 2 W-2s even though you work for the same parent company.)
