If you don't mind, I'm going to try to decipher this:
2+1+4= 7
There are 7 Princesses of Heart, but that makes little difference in this scenario......right?
13+10+8+7+2 = 40
This number does not bear any importance at all.
The last thing we can look at are the members themselves:
Roxas was the main playable character in Days.
Luxord was an active partner in Days, accompanying Roxas on many missions.
Axel was one of the main characters in Days' storyline.
Saix was one of the main characters in Days' storyline.
Xigbar was an active partner in Days. His past was also delved into briefly on a trip to Wonderland with Axel and Xion.
Again, this was just my first try at something like this. Wether this triggers some sort of epiphany or not remains to be seen. Hope it helps, and sorry for my n00bish way of looking at it! X_X
i would have to agrue on demyx as he only appeared twice in the game
xigbar only twice while luxord axel and xion are the main partners