To follow up, I reviewed the forms more closely with a Sage rep and we could not reproduce the error. That is to say, the forms were/are correct in the overall scheme of things.
I should know, by now, to check client feedback more carefully rather than take their panicked word for it.
As it turns out, I'm of the opinion that the EE with the ""defective"" W-2 simply didn't enter the data correctly in their Turbo Tax program. I seriously doubt I'll find out if this resolves the problem.