We're talking about two different things. Petipa's pieces were never under copyright, so anyone is free to alter them. Videos and most other ballets are copyrighted, so to use the them or copy tapes of them without permission is a violation of law. Authenticity may be desirable, but there's no law against updating a non copyrighted ballet.
That said, as I've said before, Petipa ca. 1950s and on is well captured on video, so we'll always have something to look back to for reference. It's not going to be lost.
Almost anytime you see Petipa's name left out it's either because the choreography is totally new or because the press person has no dance experience and doesn't realize that Petipa should be credited. You'd be amazed at how many press reps have no clue about dance - they tend to be from PR backgrounds rather than dance backgrounds. I've caught major errors by press reps for major festivals.
And I see no problem in advertising a ballet as by xxxx after Petipa because it tells you the truth about the ballet - you're going to see a version that has sections reworked by someone else. It would be worse to credit someone else's work to Petipa.
Plus, I like to the ballets updated and reworked. For example, ABT's "Swan Lake" is probably the most Petipa of any I've seen, but it's my least favorite. I like the changes and new vision that Peter Martins and Christopher Wheeldon and Sir Peter Wright have brought to their versions. If people had to do the same thing over and over again, ballet would become very stale. And honestly, when I see Swan Lake, I'm never sure what is Petipa, what is Ivanov and what was added in by various Soviet/Russian stagers over the years. What we think of as 'Petipa's Swan Lake' is probably a far cry from his original.
The RDB does protect Bournonville, but that doesn't prevent them from allowing different stagers to come and create different productions. And the dancing has changed because in Bournonville's time the women rarely dance en pointe and no-one did more than a double piroutte (no spotting). Today the divertissements are all done on pointe with much higher retire positions and more rotations in turns. Also, the Danes would probably be the first to say that they consider Bournonville's ballets as living things, and don't want them to be treated as museum pieces.
From my interview of Lloyd Riggins:
I think what people misunderstand in this theatre is that we’re not recreating what [these ballets] would look like in Bournonville’s time; we are living the process of continuing a tradition. It hasn’t died; it’s still living. And I was trying to tell the dancers especially – every time you do a performance, you have to live again inside that ballet, or else you might as well not do it.