| how did the footage viewed on Caprica contain a final cut of the documentary, including post attack scenes? |
As stated in that final scene (and pointed out above in this thread), the final cut was broadcast to the entire human fleet when it was completed. Such a broadcast could have been intercepted by the Cylons from a safe distance and relayed to Caprica. So only the footage of Sharon in the hospital, and possibly some other footage acquired before Baltar's interview, was intercepted by the two raiders.
So the Cylon raiders' primary mission was to obtain the footage that Xena-lon knew wouldn't make it into the final cut of the documentary to be broadcast to the human fleet. To get the final cut, all the Cylons had to do was to set their VCRs to record it.