If you are doing the same job since 2008 and now your reference letter should clarify that and mention that the work permit had different designations. However, in all actuality your job duties remained the same and for all those titles you can use: 2173 Software Engineers and Designers
http://www5.hrsdc.gc.ca/noc/english/noc/2006/ViewAllTitlesStructure.aspx?val=2&val1=2173&val24=*&val25=A&val26=0
Make sure to check the job description on HRSDC with your job description given by your employer.