We can take it from the mainstream media themselves that when embarrassing tapes turn out to be missing any portion, they are "doctored" and therefore discredited.  By this standard, the tape released of Mitt Romney discussing the 47% -- considered a fatal gaffe by the progs --  must be discarded.

It turns out that despite claims by Mother Jones that the tapes were presented in full, there is an obvious gap in the recordings. Benny Johnson writes in The Blaze: about the videos posted on the MJ site:

[Romney]"We do all these polls - I find it amazing. We poll all these people to see where you stand in the polls but 45 percent of the people vote for the Republicans and 48 or 49-,"

This is where the first part of the video cuts out.

Part two picks up seemingly on a completely different subject: China.

"...about twice as much as China, not 10 times as much like is reported. And we have responsibility for the whole world, they're only focused on one little area of the world, the south china sea..."

Neither the topics nor the pick up points in the sentence are the same in the two videos. Romney himself claimed this video was edited and called for "the person who has the video would put out the full material."

Mother Jones writes that the cries of selectively editing were "not true" and that Romney's comments  "were shown in full."

Back in 1992, when embarrassing tapes emerged of conversations between then-presidential candidate Bill Clinton Gennifer Flowers, Anthony Pellicano, touted as an expert on tapes, declared them "doctored" because portions were missing. This enabled the mainstream media to dismiss the tapes from the national conversation.  

More recently, the progressives worked themselves into a frenzy hitting Breitbart over publishing an incomplete recording of Shirley Sherrod. So they are on record decrying the practices of presenting less than full, unedited tapes.

Sauce for the goose is also sauce for the gander.