In some ways some of the original US stereo mixes need to be preserved too. There were often subtle differences between them and the UK stereo mixes (the ones currently available today). One example is for the original US stereo release of Rubber Soul, uniquely for the song I’m Looking Through You contains two false starts at the opening that were edited out in the UK pressing and current re-issues. This was due to a mistake on Capitol’s part where when Parlaphone (the UK distributor) edited out the two false starts, they sent Capitol the master before they edited out the false starts, and Capitol simply just didn’t edit them out because they thought they belong with the song. But as I said, all current re-issues of the album reflect the UK pressing. This flub also was only unique to the US stereo version of the album, the mono version edited them out as well.
If you don’t understand, here’s what I mean