Is This A 1909 Proof DDO

Look at http://www.coppercoins.com and see if there is a listing for this type.
It could have been due to die polishing, the removal of extra metal from die that caused the issue, vice a DDO.
It could easily be Machine Doubling as well. Or Ejection Doubling.
Look at the area in question, a DDO is typically thicker than usual and at or near the same height of the original date to be considered a DDO.

A proof is usually struck more than once to get that great detail and polished look. In my opinion, unless its a show stopping separation, its hard to say a proof has a DDO when the coin is typically struck several times on purpose. I do not, nor will I ever collect very minute doublings, thats too critical for my tastes.

When I look at coins, I follow a suggestion that was passed on to me by a retired grader;
If the variety itself requires more than 7 times magnification, then that issue is non-significant.

It looks like a contact mark on the tail of the 9.

Some info on the early proofs

http://www.lincolncentresource.com/..._Proofs.html

Great information all thanks.

Mr. Cooper, That sharp rim in the diagnostic's is an easy first thing to look at first. thanks.

Ed