A bit of a confusing post...but I think what you are saying is that after 25 years you are planning for a "big-ending" sort of adventure, and that because it is ending, that makes it 'not a campaign'?
Yeah.... Sorry. I was on my mobile and didn't realize how bad the autocorrect was until re-reading it.
No, it most definitely is/was a campaign. What I was saying was that if you had pre-planned this big ending out before the players even sat down to make characters...then it might not be a 'campaign'. I suppose that the time it takes to finish some "adventure path" storyline may qualify it as some sort of pseudo-campaign, I guess. *shrug* Anyhoo... I'm guessing you didn't "plan" this ending, or the 'core story' when you started it 15 years ago. That's the crux of the definition to me. If the DM and players go into a game knowing that they will be going from level 1 to level 20 in a sea-faring based adventure involving pirates and demons...then that isn't a "campaign" to me.
When I created the world, no. It just was the sandbox in which we played. Over time, I added lore and structure to things, including reconciling different parties (campaigns?) as being different eras and regions on the same world. I think we're all good, here.
Where I'm not sure of your definition is that, after a few years of doing other games and whatnot, I wanted to start up a new D&D game and I realized that the default assumption was that I was going to run this particular campaign setting. It actually felt a bit confining, but I hadn't quite revealed all the "secrets" I'd always wanted to and there'd been this building doom around this one dark empire. There was also a fairly unique PC concept that one of the guys had started up, but never got to play very long. So, I said, "What the heck. Let's burn it to the ground." I also told the player that it'd be a great opportunity for him to get closure on that character.
Then I invited the other players, about 2/3 of whom had played in my setting before.
So, before characters were created, I had a vague idea of where things would start, how they'd escalate, and a pretty clear idea of what the end would look like. The intent was to take the party through 20th level and, probably, into early epic levels. We ended up playing for 4-4.5 years and the PCs made it to 15th level before a combination of burgeoning families and the weight of 3.5 mechanics (for narrative gamers) made the game difficult to schedule and prep for. After a couple of particularly nasty, convoluted sessions that got us deep into rules balance assumptions vs. table expectations and style, we had a discussion about where to go and I ended up just narrating the end of the storyline. Everyone had had fun, but no one wanted to do high level play in 3.5, ever again.
On the one hand, that could be seen as the capstone for a campaign that had been playing out for a number of years, in a number of groups. It was no different than getting the PCs to name level and planning a reason for them to retire and their kids take over. On the other hand, I was pretty sure what the end looked like (success or failure) before that last batch of characters was created.
Was it a campaign?
Campaigns end. But because they end that doesn't mean they weren't campaigns. Adventure Paths end...and because they already have a beginning, middle and end, they are not "campaigns". If the DM and players continue with the same PC's after the AP's end...then it can become part of a campaign.
I've done almost exclusively home brew for my 35 year run. So, I've got no real love lost for published adventures. That said, I'm not sure I agree with your definition of a campaign.
I'm running LMoP and PotA, back-to-back. LMoP was done as a trial run of the 5E rules. At the end of that, we tweaked some build choices and decided to continue on with PotA. I do not see us continuing on when we're done w/ PotA. I just don't think I care about high-level play. For the amount of time we've spent on the game, with the same players and characters, it's more than just "an adventure". I can see the distinction of leaving the campaign "ending" open until it happens, but what do you call something that's more than an adventure but less than "open ended"?
IMO, we're still playing a campaign. It's just not an open ended campaign.