Perhaps CBS had already been told the content of the memos, or been shown the memos, but not yet received copies of the memos. This might also explain why Hodges had not been shown the memos by CBS.
A very curious aspect of this whole story is "why would Mapes be willing to jump through hoops like this for Burkett?". After all, who was Burkett to Mapes? Why would she want to do him a favor. Maybe Burkett was balking in actually handing copies of the memos over to CBS, and this favor for Burkett was a precondition for Burkett to feel comfortable actually giving the memos to Mapes. Maybe CBS didn't yet physically have the memos, and they needed to butter Burkett up to get the memos, which they got at the last moment.
It would be very interesting to know if the Burkett/Lockhart phone conversation took place before or after the docs were faxed from the Texas Kinkos.
Killian's former secretary could be the "unimpeachable source" cited by Rather. Maybe she was not shown the documents either by CBS, when they vetted the story with her, for the same reason that CBS did not actually yet have physical possession of the docs.
The above would explain why Rather repeatedly drew a distinction between the authenticity of the memos and the veracity of the story. Rather knew that the CBS sources hadn't actually seen the memos, because CBS was trying to vet the story prior to the time that CBS actually had the memos. It would also help explain why the Democrats admitted to having had the memos before CBS had them.
Maybe Mapes "needed" Burkett because he is the fall guy to be used IF problems occur. (Maybe Mapes arranged with the Dem campaign to get the documents forged. Had to be someone with a little knowledge of word processing, military lingo.)