Update!

Thank Foam and Minda.

Sale 1: https://backpack.tf/profiles/76561198002757046#!/compare/1579478400/1579564800

https://backpack.tf/profiles/76561198197891710#!/compare/1579478400/1580601600

21 keys and 50 ref = ~22

Sale 2: https://backpack.tf/profiles/76561198197891710#!/compare/1581206400/1581379200

https://backpack.tf/profiles/76561198070309970#!/compare/1581206400/1581292800

21 pure

Sale 3: https://backpack.tf/profiles/76561198337734785#!/compare/1575849600/1575936000

https://backpack.tf/profiles/76561197994783413#!/compare/1575849600/1575936000

?

Sale 4: https://backpack.tf/profiles/76561197994783413#!/compare/1576108800/1576195200

https://backpack.tf/profiles/76561198432461884#!/compare/1575676800/1576195200

?

Sale 5: https://backpack.tf/profiles/76561198432461884#!/compare/1576195200/1576368000

https://backpack.tf/profiles/76561198162683908#!/compare/1576108800/1576195200

?

Sale 6: https://backpack.tf/profiles/76561198162683908#!/compare/1576195200/1576281600

https://backpack.tf/profiles/76561198262174730#!/compare/1576195200/1576281600

?

Sale 7: https://marketplace.tf/items/tf2/984;5;u58 - 57.99/1.75 = ~33

https://backpack.tf/item/8146003402

Sellers were at 25 at the time of this sale:

https://bot.tf/stats/listings/4RGEN5L5

https://bot.tf/stats/listings/MLRE9L9J

Sale 8: https://marketplace.tf/items/tf2/984;5;u58 - 59.99/1.77 = ~34

Additional by Minda:

Two more marketplace sales:

https://marketplace.tf/items/tf2/984;5;u58 $51.99(~30 Keys using 1.71 value) and $65(high outlier)

https://bot.tf/stats/listings/MQ9O2OL1 B/O on both sales was 29, so they'll both cap.*

*Mastikhor doesn't appear in the history here since he bought it from the mannco bot, and immediately listed and sold it on marketplace: https://backpack.tf/item/3004176016

More sales:

Added 1 Key for a Pyroland Daydream Yule Hog(34 Keys)(33 Keys total)(B/O was 28)

https://backpack.tf/profiles/76561198034755171#!/compare/1583712000/1583798400

https://bot.tf/stats/listings/466R1J6Z

Sold with a Stormy Storm Killer's Kabuto for a Duped Stormy Storm Killer Exclusive

https://backpack.tf/profiles/76561198070309970#!/compare/1584403200/1584489600

Better used as a mini for that, though interestingly if we assume the best case scenario(kabuto is worth 21 and KE is worth 51), the sale will come to 29, which caps at the 28 Key B/O: https://bot.tf/stats/listings/YD1ZD20V

This shouldn't be used as primary proof, but more as support proof for the first 28 sale.

Sold to a quickbuyer for ~23 Keys

https://backpack.tf/profiles/76561198267189538#!/compare/1584662400/1584748800

Since we have actual sales now, this'll need a range of 28-29.

Classies: https://i.imgur.com/a2X5uVO.png. 28-29 it is!