Welcome!
The books are generally edited to some degree by the scanner, to trim & straighten pages, or correct color, or in some cases repair damage. Generally the books are not edited for content, other than sometimes removing pages that are not verified public domain in books that are otherwise usable. Early on it was also common to remove ad pages to save bandwidth, that has become less common as time has gone on.
Different version: This is another scan of the same issue. It is normally a new scanner doing their version, but occasionally somebody rescans a book they had done before that they're now unhappy with as their scanning skills and equipment improve. It's most commonly used when, for one reason or another, we keep the earlier version available. Some people like different scanning or editing styles, so in many cases we keep multiple versions. There have also been several cases where two scanners happened to locate and scan a missing book nearly simultaneously.
C2C: The book is Cover To Cover complete. Most commonly used to notate a scan that was previously incomplete, when the missing pages have been located somewhere, or where the original scanner has added pages that were deliberately or accidentally omitted originally. C2C normally implies there was an incomplete version previously, it may or may not be a complete rescan. We've sourced missing pages from any number of places over the years.
Upgrade: The scan has in some manner been improved, but is not completely new and in most cases is not now C2C unless this is specifically mentioned. This is something of a catch all description.
JVJ: The book scanned was originally provided by Jim Vadeboncouer Jr. He had an enormous collection of comics that he wanted to share, but no time to scan them, so he sent out his books to a large number of scanners to scan and then return to him. It's pretty much impossible to overstate his generosity and how much we have here because of him, literally thousands of books are here because he loaned them to people who generally did some slight damage scanning them, no matter how careful they were.
Hope that helps!