Not to nitpick too much, but this is a pretty inefficient way of using your credits. A better way would have been, at the end of each cycle (after opening the loot boxes), to check the total value of the wallet against the total cost of the unobtained items and end the simulation if the value is greater than the cost.
Basically, you want to save all your purchases for the end, if you're going for 100% completion. That way you never get an item that's a duplicate of one you bought. Your way just wastes most of the early credits. Since you're going to be buying the last few dozen items either way, saving all those early credits to do so is the way to go. If the average item costs a couple hundred plus credits by then, then, e.g., 50 "must-buy" items times 250 credits, cut by a fifth to account for duplicates of purchased items, divided by an average of say 40 credits per box, and you've "overworked" yourself by about 250 boxes.
It's not a huge cut from your overall calculation, but it's still a pretty significant amount.
tl;dr: Yatzhee's estimates should be cut by about 10%.