The Chance of Getting Tier from the Great Vault on 9.2 PTR - Observations and Remaining Questions

wowhead.com:

Tier Sets have started to drop from the Great Vault on the 9.2 PTR and we've opened 200 Great Vaults to estimate the Drop Chance of tier pieces showing up in the Great Vault!

As Blizzard did not reveal the exact drop chance of Tier in their Tier Set FAQ earlier today, we took to the PTR to estimate what the drop chance of Tier will be in Patch 9.2. However, Blizzard is the only one that knows the exact drop chance, and this is only an estimation. Data was collected using a Brewmaster Monk using exactly 1 box in the Mythic+ row. If the drop chance is different between each form of content, or with additional boxes amongst the same row then this data will not support that. In addition, as this was tested on the PTR, this may change going forwards.

Opening the Great Vault 200 times on the 9.2 PTR, we received 12 pieces of Tier Gear which works out to be an estimated 6% Drop Rate for this slot. Using the sample size and observed drop chance, it's likely that the drop rate is somewhere between 3% to 10%. We received:

From this data, we'll be proceeding with an estimated 6% drop chance from the Great Vault. Here are some thoughts based on the data:

From the above loot that we received, it appears that the Great Vault can presumably drop Tier Pieces from any boss in Sepulcher of the First Ones, even bosses you haven't killed (was done on a character which did 0 raid testing). This means that the Great Vault could give you a Tier Chest or