Yes, they are best described as spin-offs. And yes it is an expanded universe of Final Fantasy VII. However, this expanded universe cannot be entirely canon when considering it alongside the 1997 Final Fantasy VII because there are notable differences between the two. Thats why they can't act as fillers between the games.I keep telling people: the Compilation is an expanded universe. It's canon, but not on the same level of canonicity as the original game. Why? Because not one of them has been an RPG. Unlike FFX-2, they are not true sequels or prequels but spin-offs. The only way FF7 will ever have a true sequel will be if there is another RPG with the same elements of a normal Final Fantasy game. (And preferably entirely independent of the Compilation. It can rely on the Compilation as filler between the games, but the plot should be entirely understandable without it.)
As a Compilation Hater I'll answer your question. Advent Children also add twists to the FFVII plot; however those who accept The Compilation don't seem to notice that too often. This is probably due to Dirge of Cerberus' vast amount of retcon even when compared to the rest of The Compilation. I must admit, Advent Children look ace and it is fun to watch. But I like the original plot of FFVII more and so choose to put AC together with the rest of the spin-offs.The problem is when some people decide to ignore things like Ultimania Omega Guide and Reunion Files. These two books aren't prequels or sequels. They don't add any new plot or characters in the story(of FFVII and AC). They just give the answers to most of our questions. But Compilation Haters don't want to accept these answers. Why?
I'm rejecting the future information because it is retcon. I presume the point of this example was that the poison did most of the work, yet the stab was what ended it? FFVII had a complex plot yes, but like I said earlier in this topic, most of the answers to the difficult questions are in the game. They are tough to locate though, because they're scattered among various pieces of text that apparently is no where near where they "should" be.To ignore the compilation would be the same as to do this.
A murder victam was found stabbed and had been stabbed in the side. The presumed Cause of death was the stab, however during the autopsy a deadly poison is found in his system, and presumably the poison had been in there long enough to kill him the day before his body was found. However, they still report Death by Stab wound, and ignore the fact he was poisoned. You are doing the same thing by rejecting future information and assuming it is false while the old information is true.
Yes, this example is extreme, but I work in extremes.
Btw, I would love to read the Jenova theory but it requires a password I don't have. I guess you brought it up because you believe my version here to be wrong? Well I'm always open for discussion.