Stampers (the plates with the inverse patterns of the disk's faces) are mounted into a record press at the beginning of a production run. During a production changeover people are generally paying attention so the chances of actually having wrong sides on a disk are very minimal. (Which is why, as Bryan mentioned, it would likely be worth a lot.)
Labels are loaded on the fly, as each disk is pressed, usually by hand (the loading, not the pressing). So it's not surprising that out of the thousands of disks any given (not well paid or well treated) factory worker churned out an occasional label got mixed up.
Double labels and off-center labels are also seen here and there.
JPSmit said:
Saw In interview recently with a guy that owns a factory that makes records and CD's.
Back in the eighties and nineties, when he was at a party or whatever and somebody asked what he did their next question would be "they still make records?"
There's been a resurgence of vinyl lately. His production volume of records, which took a big dive in the eighties, is back up to where it was sometime in the sixties.
With the onslaught of MP3's and downloads, when he tells people he makes records and CD's their next question is now "they still make CD's?"
pc.