In the past, since the V1 was launched, shell designs were usually (but not always) grouped by region:
However, there were exceptions to these groupings, so as far as I can tell, BanDai had no "hard and fast" rule whereby European versions always were different from North American versions. So I don't think there is an official "breakdown" - unless you have access to BanDai's marketing plans for each of the versions releases by region.
The shell designs (choice/colours, etc.) varied by geographical region and by version release. I think it had a lot to do with the number of shells that were being manufactured for a specific version based on how popular a toy they were at the time of marketing.
The V3, V4, V4.5 (in particular) all had a huge number of shell designs and variations - the "star" antennae and "ball" antennae were interchanged on the V4 and V4.5 in the European region for example. Compare that to the V1 which had some shell designs only available in one region mixed in with a few designs that were also available in two regions - several of the European V1s had the same shell as the Japanese Plus for example.
In addition, I know that when the V1 was released in Europe and really took off, the demand far exceed supply in my country and after about 6mths one of my local toy stores was offering north American V1 Connections for sale alongside the V1 Connexions that had previously been released in Europe. I think BanDai organised to have some shipped across to meet demand.
Add to that the international selling and buying that goes on with auction sites like ebay, then you have a situation where any design released in, say USA could be purchased by a European or Australian resident, so pretty much everyone has access to most of the shell designs if they are up for sale on auction sites.
Edit: In case you haven't seen it and it is useful to answer your question: http://www.tamatalk....-designs-v1-v4/
One of our members, ciara683 made up a list of all the North American shells from V1-V4 - it's pinned in the Tips and Tricks forum.