Even though the movies are numbered 1-6, the real watching order is still 4, 5, 6, 1, 2, 3. Do you think it was an accident they were filmed in this order? It's sort of a big flash back to see how you got there.
Heck there's still the 7, 8, 9 that may or may not happen. The original plan was 4, 5, 6, 1, 2, 3, 7, 8, 9.
As crazy as GL is now, he USE to be a real sharp filmmaker.
Once he falls on his face as the "serious" art-film maker he's "retiring" to be, he'll film 7, 8, and 9 to pay his bills and stroke his ego.