Please read the links
http://en.wikipedia.org/wiki/Iraq_Campaign_Medal <--Created in 2005 then retroactive
http://en.wikipedia.org/wiki/G..._Expeditionary_Medal <--created in 2003
When the wars started in Iraq and Afghanistan, no official campaign medal was established. The GWOT-EM was created for recognition for those deployments before the ICM/ACM was officially approved by Congress.
They made the award retroactive for those people who wanted that recognition who was still serving or left the service. It was up to the servicemember if they wanted their GWOT-EM changed to a one of those campaign medals (obviously they had to meet the requirements for service in Iraq or Afghanistan). The GWTEM ribbon was/is still given to people who went to Kuwait, Qatar (remember the SOCCENT base in Qatar shown in Transformers) or served in Cuba under OEF. Years back, you could of earned both, if you were deployed to Kuwait and then got sent north to Iraq and Afghanistan for some months, then under that scenario, you will rate both and your ERB will have the OS breakdown to reflect that. I know a SFC that did.
It is very easy to understand. You either remain with your GWOT-EM or get it changed (you go with one or the other, you cannot have both). If you do get it changed, then if you go to Iraq now, it will be your first GWOT-EM medal. If you remained with your GWOT-EM, then you simply add a campaign star to it.
You rated and earned the GWOT-EM for your 2004-2005 service. And you could have gotten it to the ICM if you wanted to. I arrived to Iraq in August 2005 and if you read that wiki, it was officially distributed in June 2005. By your date, you already re-deployed. I received the ICM when I left Iraq in August 2006. I do not have a GWOT-EM and with the number of ribbons I have, I really do not want another lol. I just earned a Korea service medal recently and if the stars align, will retire without going back downrange.