Don't know if it's true or not, but according to Theodore Gracyk's book, Listening to Popular Music, Or, How I Learned to Stop Worrying and Love Led Zeppelin, in the studio the acapella bits have a measure of 5/4, but live, they changed that to 4/4 so the band were more assured of all coming back in together.I believe even Led Zeppelin had fun trying to replicate the recording. If you listen to the tune from IV and then listen to the live versions they've done you will hear that they don't do the pauses the way they did them on the record. At least this is what I've found when I learned to play the tune for my band. I learned most of it from the record. Then I figured out the breaks from the live versions. They are not the same. When they play it live they don't pause but play the next line in time. Unless I'm cuckoo for cocoa puffs. Which is highly probable.