So far the only stupid person here has been you. The glitch he is talking about shows xur offerings from different points in time. Because it is displayed through his window we can consider the items displayed as possibilities at any given time. It would be much more worrisome if those items were never seen, at that point you could assume the item being looked for was not in his loot table.

I apologise for offending you, but this is widely considered to be fact, but if you would like me to recalculate i can, 4 exoticshave been sold by xur for warlock. 1/4: 25% chance 25% = 0.25 0.25 * 0.25 * 0.25 * 0.25 = 0.00390625 0.00390625 = 0.390625% chance of it being sold, assuming Xur only sells these four exotics, still around a 3 in 1000 chance