Tax time, just received my group certificate and when I opened the envelope I found two in there?

I work for the same company and have been with them for just over 12months. They have two different company names on them and two different ABN numbers. One said i started on the 8 July 2009 and worked till the 30 June 2010 and the other one says i worked from the 7 October 2009 to the 30 June 2010. Does this mean the taxation department will think i worked two jobs? If so will i have to end up owing them money? As i said it is the same company i work for and i did not even know this would happen.