For those with DIN access, the following sites sum things up nicely:
SWASM
In short, awarded to those who meet the following criteria:
The South-West Asia Service Medal is awarded for a minimum of 90 days cumulative service in direct support of operations against terrorism in South West Asia from 11 September 2001 to 31 July 2009. Direct support occurs when a member is deployed to a unit or organization outside Canada but not into a specific theatre of operations, and where his or her primary duty is to provide direct assistance on a full-time basis to the operations against terrorism in South-West Asia.
The medal with AFGHANISTAN bar is awarded for 30 days cumulative service between 11 September 2001 and 31 Jul 2009 in the theatre of operations, which is a subset of the United States Central Command Area of Operation Responsibility (USCENTCOM AOR). The theatre of operations is defined as the land, sea, or air spaces of Afghanistan, Bahrain, Kuwait, Qatar, the United Arab Emirates, the Persian Gulf, Gulf of Oman, Arabian Sea, Gulf of Aden, Red Sea, Suez Canal and those parts of the Indian Ocean north of 5° South Latitude and west of 68° East Longitude.
Rotation Bars are awarded to recognize a further 180 days of eligible service following qualification for the Medal with AFGHANISTAN bar or the last Rotation Bar the person has earned. One bar bearing five maple leaves is worn in lieu of five bars bearing one maple leaf.
Note that those who received the SWASM without the AFGHANISTAN bar are not eligible for Rotation Bars
General Campaign Star - South West Asia
In short, awarded to those who meet the following criteria:
with the Canadian contribution to the International Security Assistance Force (ISAF) in Afghanistan for at least 30 days cumulative between 24 April 2003 and 31 July 2009, in the theatre of operations which consisted of the political boundaries and airspace of Afghanistan; and/or
in the theatre of operations consisting of the political boundaries of Afghanistan, the Persian Gulf, the Gulf of Oman, the Gulf of Aden, the Red Sea, the Suez Canal and those parts of the Indian Ocean and the Arabian Sea that are west of sixty-eight degrees East longitude and north of five degrees South latitude, as well as the airspace above those areas for at least 30 cumulative days commencing on August 1, 2009, provided that the service has not been recognized by another service medal.
So, up to and including 31 July 2009, there were two medals that service members could be awarded, depending on "stuff".
Those who serve from 01 Aug on, there is just the GCS-SWA.