You may have dificulty getting TurboTax to e-File a second time the same amendment.
One way to verify the withholding is to supply to IRS your fed copy of that tax document showing withholding.
You can supply that by mail attached to another 1040-X with an explanation.
Call it "Amendment No.2 supporting Amendment No.1 with supplement"
Note: when you are not changing any dollar amounts on your amending 1040-X, you can leave all the lines 1-23 EMPTY.
