Well as it goes for drop buffs, I am almost sure, that they are not changing loot type at all.
As for mobs/bosses "loot table" looks something like that:
-rune (stat)
-rune (production)
-white (item)
-green (item)
-blue (item)
-pink (yeah I know purple

) (item)
-special items (like quest/event...)
Each of this item has some % chance to drop, currently I am pretty sure, that collecting more than 2 items same color, is because you have multi stage drawing. First is simply if you get item and second is what item will it be. So you will get let's say 30% chance of getting first item, with drop buff (300%) it would be 120%, so 1 item is for sure, second item is 15%, so with loot buff 60%, 3-rd 7,5/30, 4-th 3,25/15 etc. (only example). Lets go on - you get 3 items, so second stage drawing is 10% for pink, 20 for blue, 30 for green and 100% white. Of course there is probably some max, but rest works same.
It also seems, that prod. runes have another drawing only for them (quiet reasonable, as you can get more than one each time.
Of course it can draw item right away without is there/is there not item, so simply 5% purple, 10 blue, 15 green and 20 white, but still from the point of drop buffs everything works same (well some part changes - later on).
There is also some max no. of draws - probably strongly depending on type of enemy (boss/mob/elite...) or even each enemy (by name) has own number.
For dura I am testing for some time now, a trick with roll function and at current stage I am pretty sure, that durability base on same function - XX+roll probably (maybe even client side). Where is drop buff there? Well back some time, while DoD farming I have observed that with lucky potion I get more items (difference was not so big and probably some bigger scale testing would be required, as It could be that I have few times more luck, but during this few tests - it works always). As I said small difference, but +5 dura would be fine to me (currently exchanging memo I am always full buff)....
Here goes most important (I think so) part. Older instances have chance of purple<100%, so drop buffs enhanced that chance of getting any. In newer (since HoTo I suppose, maybe HoS or TT?

) you have 100% chance of getting purple item(s) and you always get same no. of them (1 or 2), so there is possibility, that item is not drawn at all.
So it is highly possible, that items are drawn while entering instance in the past you simply have 1% chance for purple, 10 blue...... The key thing could be, that it could be done at least 2 ways. 1-st and 2-nd same color item could differ with % of chance drop, so purple 10% drops to 0,1 green 50 drops to 25.... second and more likely to be is that it is rather XX-YY%, so purple 10-10, green 50-15... (with minimum of 0%).
As I farm a lot, I have not seen a big difference with drop rarity while w||w/o buffs. So the difference is small or there is no difference at all (of course blues drops more often, but whites also), some small difference with honor PT, but it is not quiet drop buff. It makes me think that drop buff do not change chance of looting each color item (as there would be more blues and greens), but no. of draws (as in the beginning of this post).
So definitely drop buffs gives almost nothing on "modern" instances. Dura relies on roll+really small on drop (potion from housekeeper would be OK, as it is for free, but nothing else). And item drops always anyway. The question is about stats, but i suppose again roll and 0-xx - stat1, xx-yy - stat2....
Back to the main topic... I think there is possibility that instance ID determines drop. Of course it will be very difficult to determinate where drops what, but as we have 4 types of clothes and from one boss usually drops one, than I suppose 1-2 months DoD farming would be enough to find out some pattern, as I suppose it probably works on every instance same and even if not finding pattern to new instance shouldn't require that much time.
It would be probably some kind easy, as the no. of instances are reseting each day and dura is different function (probably - as my tests show something like that).
It would be probably even easier to do this that way, as there is only roll left and drop changes it a bit, so full buff would reduce drop of some items and producer would have problem which?
So if some time ago someone get knowledge how to read drop from instance ID, it probably wouldn't change and even if it will be probably small modification, so again few days/weeks and new formula would be known.