My thinking is this: A random numbre generator must be creating different numbers constantly. This random number generator works off the clock (what easier way to have a constantly changing base number?)
Stuff such as item drops, upgrading, and socketing rely on these random numbers, hence why so many people believe at different times you get better drops, more sockets, and easy upgrades etc...
Only thing is, where are these numbers?
Its possible the chance of upgrading lvl with mets, and quality with dbs in tc could overlap, so using the 1-3 mets on the item is a way of testing whether your item is within this lucky time frame. Its also possible each item type has a different time, as this would make things more random, hence harder for people to latch on to the pattern. If youve read entire post, most people who have said it worked, metted and dbed same item, and some people who failed used different items. Think of it as a span of time which decreases as the chances get less.
Eg. If a Lvl 5 blade has a 99% chance of upgrading to lvl10, then 59 secs out of 60 (im just using it as an example, it may use seconds) meaning if the time was ??:00-??:58 it would upgrade. Now using a elite Lv 110 blade, it may only upgrade when time is ??:00-??:01, and fail when its ??:02-??:59, hence chance is 2/60 (this just being an example, not actual figures)
Now if the chance of upgrading quality with dbs on a lvl 5 normal blade is 70% (lets say), it would mean between ??:00-??:42 it would succed, hence testing it with mets first would mean between ??:43-??:59 the mets would still work, but the db wouldnt.
In the case of the L 110 elite blade, say the db would upgrade quality with a 8/60 chance, so if a met you use succeds, (at ??:00-??:01) you would have only until ??:07 to use db to get a sure-fire upgrade..
Is this making any sense?