My previous expirience has been:
MA: awarded SSHRC, not OGS
PhD 1, PhD 2: awarded OGS, not SSHRC
PhD 3: awarded OGS and SSHRC (this competition)
I would think that once you are awarded an OGS for your project, the results don't change much as long as you keep up the same level of work, the same general project, and same standing in your department. I know of fellow students who didn't get OGS after having received it in previous years because they started to slack, didn't follow through with publications, got in tiffs with department heads/profs, etc--in this case, they are often downgraded from top 2 or 5% to lower...which significantly effects their chances. New grad students (a particularly strong or weak year) can also completely distort departmental rankings. I was told (problematically and unprofessionally) by a professor at my school that the majority of the new PhD 1s outranked the PhD 3s in their applications.