Hey Karo, I'm in Santiago, Chile. I'm pretty familiar with most of the MAC employees here and they've told me B.A. gets its stuff from Chile, where the Southern Cone office is. If that's the case, I can tell you that many of the collections come out only a week or two after they come out in the US and some even come out ahead of time.
For example, I got the new pigments from Sundressing, the liner from Technacolor and the MSF from Avant Gold about a week before they were released in the US!
Other collections, like Lure for example, were released about 2-3 weeks after US release date. At most, release dates are a month behind, not much more than that.
The only drawback is that we don't get every collection and some releases don't include every single product in the collection. For example, for Patternmaker (and basically, the yearly Nordstrom anniversary collection) they only have the palettes and the brushes/bags. They've never had the blushes and glosses also released in those collections.
Hope that helps!