Nice math and thought behind this assumption. But this only applies if you look at it as 4 weeks and not as week by week. If that were the case If you're looking at a clump of weeks rather then one by one I would suggest looking at EVERY week xur has ever sold. Keep dating back and count them up because you can't just choose 4 weeks and say it's not possible! Either is Week by Week or Beginning of time for Xur. That's the choices here and if it's from the beginning.. xur can be dated back 3 years + in which case it doesn't sound unreasonable for him to sell them 4 weeks in a row (Also he sold 2 then sunbreakers and then 3 not 4 in a row http://destiny.wikia.com/wiki/X%C3%BBr/Visit_History) If you look at it at a week by week basis then technically everything has an equal chance to be sold and it would make perfect sense that something could be sold 3 times in a row if you looked at my algorithms in my topic. Giving items multiple "Roll numbers" would mean they have greater chances. If VV had 5 chances same as the rest then each week it is possible to roll 3 of those needed numbers to get the item to be sold. It isn't that hard to believe it could be sold 3 times in a row. But if you look at the percentage of it being sold 3 weeks in a row and only those 3 weeks you will see a slim percentage but thats on the basis xur was only ever around for 3 weeks and that the game knows what the past week sold. If that was the case then bungie could easily implement a "wall" that prevented such things happening but since it works week by week (That's what I believe) there is no such thing needed.