question about EB1A: the date of recom letters

Need help from experts:
Got support letters from my references dated October, 2006. The letters were meant for Outstanding Researchers (it specifically stated xxx is an outstanding researchers etc).
I didn't get to EB1B for some reasons.
Now I am preparing for EB1A. Can these letters be used for the EB1A petition? Do I have to ask them to write new letters?

Thank you very much. I really appreciate the help.