Perhaps you can provide the link that you checked the union numbers against?
Seeing that the numbers are precisely the same over 1980-2004 and looking through other documents on BLS which also correspond perfectly with the earlier data on 1964-1979, I must admit that the original numbers are entirely correct. I'm no union fan--never been in one.
On your computer screen, place the straight edge of a piece of paper along the Sept. point of the previous year to the one which you're checking in the chart. Then move it to the following Sept. point.