Most of the things I've referenced have slightly different art, watermarks or even just print colours from different batches. A lot of people call themselves completionists but give themselves contradictory rules over what they think is necessary to collect (or sleep at night); which I'll waffle on about shortly.
For me, I find it interesting being aware of these differences. All together, they tell the Story of the game of Carcassonne. Knowing that expansions were altered and the reasons why they changed is interesting; at least, in my opinion.
Just this week we had a conversation about the 1st and 2nd Edition of the Winter Edition from Z-man games. The first contained the Gingerbread expansion, the 2nd did not and the box art was changed to reflect this.
Some changes are unintentional. Correcting a mistake between print runs (like the Gingerbread), or perhaps subtle changes in the factory's manufacturing process (such as the Teachers) or Crop Circles [there are 3 colour variations of CC1].
In my opinion, people who buy stuff operate at different 'levels' and swap and change between them as they feel fit.
For example: the first level (in my opinion), is the 'rules complete' collector. These collectors can have one of every tile, regardless of artwork and be happy knowing they can play the game and invoke all the rules as they feel fit. In my opinion, this means they wouldn't care if they had: cathars from spielbox or the siege tiles from CSC. Granted the rules are ever so slightly different, but the tiles permutations are identical - just with different artwork. Similarly, these people don't care if they have a red or blue teacher meeple. They are all the same. Similarly, phantoms from a Red or Green meeple box are identical.
Those nuances I described above, lead to the next level of collection; which this is probably the level we are likely to reside in. It is also the level which is hardest to quantify. Some refer to it as the 'one-of-everything' level, but I think this is incorrect. I like to refer to it as the 'conscious differentiator'. You make decisions over what you need or don't need. You're the person that needs all 5 teacher-meeples. You're the person that needs all 5-phantom boxes. You need siege AND cathars, because they're different enough. You needed the Russian promo-tiles, even though they're the wrong shape and have 'K's on the back. You can probably live without: the colour variant of Crop Circles, you don't need a correct BS&B tile, you don't need the pre-corrected Inns and Cathedrals CRCr tile, with the bush, you don't need early non-watermarked expansions. Possibly you don't need Carcassonne 2.0.
This level of collection is hard, because most of the subtle differences are accidental between publishers and print runs. Also they're not documented very well.
You may, for some reason you NEED the 70-point score tile, even though, it makes no difference to the game. In fact, the 70-point score track is a bit useless. The 49-point score track is superior in a number of ways. For a start, 49, loops back around to 0. Also, have you noticed the low score spaces are bigger than the higher ones? It's because you're more likely to share a score of 0-12 at the start of the game, when a small city or a road is completed early on. Later, you're less likely to share a score of 35, when the game is underway, so you don't need to take up as much space to share meeple. I find this level of aesthetic-engineering in a game ultra-pleasing. There's also some psychological arguments made, that suggest players look closer than they are, between 20 and 45, to encourage the competition. The 70-point score track is rubbish in comparison, it doesn't loop and all the spaces are the same size. Personally though, the gray 49-point score track is my favourite, I find the scores easier to read.
Perhaps it would be nice if Hans im Gluck reprinted this scoreboard for the celebrations this year? Would that put our collective-itch to bed? This really takes us to that next level of collection - 'the true completionist' (the I still need a 1st Edition collector!)
As I said the 'conscious differentiator' is the hardest collector to define. They (myself included) are able to justify the reasons why they either need, or don't need an observed variation.
A post somewhere on here, or CarcF listed all the known releases of the base game box. There are approximately 12 now. The cover artwork has been changed at least 4 times, that I'm aware of: The bearded-thief, the lady, the smiling knight and lady, and Hans (of Hans im Gluck) riding a pig in the background. There are numerous changes to the box-back art as well, and the various iconographic changes.
These changes, are insignificant to the game, but as I said before, tell the story behind the game of Carcassonne. I assume the thief was changed to a female to appeal to female gamers. I find these sort of changes interesting. I'm not sure about the reason for the pig riding.
To finish of my incoherent ramble - I hope in the coming months and years we'll have a better archive of all these minor variations, so that collectors at all levels can review their collection and identify what they own (or have the potential to own, if they desire) all these subtle variations.
+1 for HiG reprinting the 70-point score board too, for Essen this year
