What purpose did Quaid serve Cohagen as an Average Joe on the assembly line?

I can't say anything for the 1990 version, but I don't think step 2 was included in the 2012 version. I could be wrong, but my understanding was that Quaid worked for the rebels knowing he was a double agent. The video recording that was activated by playing the piano had Quaid stating that he was Cohagen's agent with the mission of getting close to and killing the rebel leader. He said that this mission changed when he met Melina, and she showed him the "truth" about the rebels. So, we are lead to believe that Cohagen realized Quaid had turned, so he gave Quaid the false information about the kill code as an unknown source of disinformation. Then, to make the disinformation seem real, Cohagen captured, brainwashed, and hid Quaid from the rebels. By doing this and having the "wife" complicate things, he made it seem that the info Quaid found out was very important. Once the rebels got the "average Joe" Quaid to the rebel leader, they tried to access the information about the kill code in his brain. But, this just allowed Cohagen to trace the location of the rebels, since the code doesn't exist. In the 2012 version, it seems that Cohagen played Quaid from day one.

So, for the 2012 version, the purpose Quaid served as a factory worker was to be a "trojan horse" and unknowing double agent after he was brainwashed. This allowed Cohagen to pinpoint the rebel leader's location and kill him.